CHAPTER VIII · The geology and geography of Northern Nigeria

TERTIARY VOLCANIC ACTION

Absence of pre-Tertiary volcanic rocks within the Protectorate: two periods of Tertiary volcanic activity. The early Tertiary period: the Maradu vent; the nepheline basalts of Wase and Tangalto; the phonolites of Wase Rock, Tangale Peak and Bantaji; the plateau lavas of southern Bornu, Bauchi and Nassarawa; petrographical character of the lavas; early Tertiary lavas of the Sahara, Sudan and Adamawa. The later Tertiary volcanic period: the puys of northern Yola, the middle Benue valley and the Bauchi plateau; petrographical character of the lavas; petrographical provinces.

It may be presumed that the intrusion of the alkali granites and dyke rocks throughout the Protectorate was accompanied in pre-Cretaceous times by considerable superficial volcanic activity (p. 142). M. Chautard[172] has, moreover, described the intercalation of volcanic rocks in the Upper Cretaceous of Senegal. All trace of pre-Tertiary effusive rocks, however, within the Protectorate appears to have been removed in the course of denudation. The fracturing and folding of the crust at the close of the Cretaceous was apparently accompanied in places by the formation of mineral veins within the fissures, but no contemporaneous igneous activity has been definitely identified within the Protectorate (p. 140). Within the Tertiary era itself two separate periods of volcanic activity may be recognised, one in the middle Eocene and probably to some extent contemporaneous with the accumulation of the Eocene sandstones within the Protectorate, and one in late Pliocene or early Pleistocene times and contemporaneous with the later Tertiary oscillations of the crust. For the most part the eruptions were of an isolated character and gave rise to the formation of detached pipes, cones and puys of igneous material. More rarely, as in southern Bornu and on the borders of Bauchi and Nassarawa, the extruded lavas united to form a continuous sheet of volcanic rock, which covered a considerable area of the underlying sedimentary and crystalline rocks.

The earliest outburst of volcanic activity appears to have taken place towards the close of the post-Cretaceous erosion or possibly in the middle Eocene at a period contemporaneous with the accumulation of the lower marine beds of Sokoto, and is represented now by the extensive neck or vent of fragmental material near Maradu in Sokoto province whose levelling was accomplished during the later extension of the middle Eocene sea. The greater number of the boulders in the agglomerate are composed of a microgranitic quartz porphyry with phenocrysts of orthoclase, biotite and brown hornblende in addition to quartz (1323). To the same period is probably also to be referred the line of well-worn stumps of basalt, phonolite and trachyte which stretches from the Gongola valley westward through Tangale and Angass to Namu in northern Muri. The Tangale Peak (Pl. XIII, Fig. 2) and the Wase Rock (Pl. V, Fig. 2), which still retain a portion of the original flow attached to the rock in the vent, were probably among the latest eruptions of the series. The intrusive dolerites of Bashar (41) and Awe (1014) may be ascribed to the same phase of igneous activity, while the Rock of Bantaji in Southern Muri may be taken to represent contemporaneous volcanic action to the south of the Benue.

In petrographical character the basaltic pipe rocks are always olivine- bearing and usually porphyritic with olivine and augite. Felspar is found only in the ground-mass which at times contains a little intersertal glassy base. The basalt of Wase Topa is remarkable for the number and size of the nodules of olivine which it encloses. A worn vent immediately south of the town of Wase is filled with a fine-grained nepheline basalt (32) containing glomeroporphyritic aggregates of augite crystals and well-formed crystals of olivine. Felspar is entirely wanting, the ground-mass being composed of small rods of augite and granules of magnetite set in a brown glassy base studded with minute crystals of nepheline. A somewhat similar but coarser-grained rock from Tangalto (1661) contains large crystals of decomposed olivine and purple and well-zoned augite in a holocrystalline ground-mass of rods and granules of augite, magnetite grains, flakes of biotite and abundant nepheline in well-formed and irregular crystals. The nepheline was evidently the last to crystallise, and to some extent takes the place of matrix, being in part moulded upon the other constituents of the ground- mass.

The phonolite of the Wase Rock (31) is of a trachytoid type, containing columnar phenocrysts of sanidine, ragged crystals of ægirine augite and scattered pseudomorphs after nepheline in a ground-mass consisting predominantly of minute felspar prisms with a well-marked fluxional arrangement, mingled with magnetite grains and rods and granules of green pyroxene. The phonolite of Tangale Peak (1665–6) contains phenocrysts of sanidine and soda pyroxene in a ground-mass of a more orthophyric type, composed of minute idiomorphic crystals of nepheline, imperfect prisms of ægirine and ægirine augite and elongated microlites of felspar which pass into an ill-defined felspathic matrix. Traces of brown hornblende in irregular porous growths may also be observed in the ground-mass. A similar rock from the immediate neighbourhood of Tangalto (1663) contains soda pyroxene, but no evident nepheline in the ground- mass, and may be grouped provisionally as a trachyte. The phonolite of Bantaji Rock is of a more nephelinitoid type, with the ground-mass enclosed in a somewhat intersertal manner between the abundant but much decomposed phenocrysts of felspar. With the felspar are associated as phenocrysts hypidiomorphic crystals of ægirine and ægirine augite frequently in zonal growths and smaller idiomorphic and abundant crystals of somewhat weathered nepheline. The ground-mass is composed of lath-shaped felspars, granular pyroxene and irregular patches of analcime probably of secondary origin. The association of phonolite and nepheline basalt, observed in the neighbourhood of Wase and the Peak, has not been recognised around Bantaji.

The period of formation of the lava fields in southern Bornu and on the borders of Bauchi and Nassarawa may be provisionally referred to the close of the middle Eocene, on the strength of the apparent intercalation of a friable red sandstone amongst the lavas in the escarpment of the Barbur plateau behind Dukshi. The extensive erosion which the plateau lavas themselves have undergone indicates, moreover, that they are of no very recent age. The eastern lava field is the more extensive of the two and perhaps somewhat younger, so far as one can judge from the less denuded character of the cones. The rich content in iron of the upper part of the Eocene accumulations may possibly have been conditioned to a considerable extent by the distribution of much fragmental basic igneous material upon the surface of the waters.

In petrographical character the lavas are basaltic throughout and rich in olivine, and vary from felspathic doleritic types to limburgitic varieties in which felspar is greatly reduced in amount.[173] Nepheline- bearing types have nowhere been recognised, nor any effusive rocks more acid than basalt. MM. Chudeau and Gentil[174] have, however, indicated the occurrence of ægirine rhyolites and phonolites, as well as of basalts, tephrites and limburgites, amongst the older lavas of Ahaggar and Air, which are probably of similar age to those of Nigeria. Dr. Passarge[175] has described the occurrence of basalt, augite andesite and phonolite on the summit of the Shebshi hills on the borders of Nigeria and the Kameruns. MM. Gentil and Freydenberg[176] believe that the ægirine porphyries of Mounio and of Hadj el Hamis on the southern shore of Chad are of volcanic origin. M. Garde,[177] however, is of opinion that they possess an intrusive character and belong to the hypabyssal phase of the alkaline magma which gave rise to the Mounio and Melfi granites.

The plutonic rocks of this early Tertiary volcanic period are nowhere exposed within the Protectorate, and hypabyssal types are almost unknown. The doleritic sills of Awe and Bashar were probably injected during one of the earlier phases of igneous activity. Dr. Passarge[178] has indicated the occurrence of basaltic dykes in the sandstones of Adamawa and a boss of nepheline syenite between Yola and Garua on the upper Benue. The latter, however, more probably belongs to the underlying crystalline floor. M. Chudeau[179] believes that the alkali granites of Zinder and Mounio have been intruded since the close of the Cretaceous; but while there is every reason to believe that the nepheline basalts and ægirine rhyolites of Tertiary age drew their origin from a magma rich in soda, there is, as already stated (p. 140), no evidence within the Protectorate upon which any immediate connection between the younger soda granites and the Tertiary volcanic rocks can be established. On the contrary, there would appear to have been in the middle Eocene within the Protectorate merely a renewal of volcanic activity from the same alkaline source from which the pre-Cretaceous granites and dyke rocks originated. If, however, further investigation should confirm M. Chudeau’s suggestion of the Tertiary age of the granites and porphyries of Zinder, Mounio and Goure, these rocks may then be taken to represent the plutonic and hypabyssal phases of this middle Eocene period of igneous activity.

To the later Tertiary period of volcanic activity, which may be referred to the close of the Pliocene and which perhaps also extended into the early Pleistocene, are to be assigned the puys of Kereng (Plate X, Fig. 2) on the southern margin of the Bauchi plateau, the puys of Song and Mboi (Plates VI, Fig. 2; VII, Figs. 1, 2) in northern Yola, and somewhat doubtfully also those of the Awe district on the middle Benue (Plate V, Fig. 1). The puys of the Kereng group are remarkably perfect and exhibit steep crater walls of fragmental material breached by a single short flow of olivine basalt. Elsewhere on the plateau also, as between Vom and Bukuru, there are small puys with breached craters which are probably of a similar recent age. From the cliffs of Assab, moreover, later flows of lava may in places be seen on the worn slopes of the plateau edge, and there is every reason to believe that the erosion of the drift and of the margin of the plateau was considerably advanced before the final close of volcanic activity. The presence of craters and the local character of the associated flows serve to distinguish these later products of igneous activity from the earlier lavas of the plateau. A similar superposition of later volcanic material upon earlier lavas has been observed by M. Chudeau[180] in the Ahaggar and in Air. Unlike the central Sahara, however, there is in Nigeria no reason to believe that there has been any actual continuity in volcanic action between the earlier and the later periods.

In Yola province the Mboi Hills are crossed by a line of small craters four or five miles long, running roughly in a N.W.–S.E. direction. To the south-east between the Mboi Hills and Song the line is continued by a number of hillocks of basalt for a few more miles, but how far it extends to the N.W. is not known. Only a relatively small amount of basalt was erupted from these vents. In the case of the largest crater with a crater floor of 250 yards in diameter the volcanic material was not sufficient to conceal the granite through which it came. The granite was broken away during the eruption so as to form a cliff extending one- third round the crater, while the other two-thirds is formed of agglomerate and tuff with very many fragments of granite. The crater thus resembles a swallow’s nest attached to its support. With one exception, where the wall is entire, all the craters were breached by a lava flow. They are in excellent preservation, and the cliff-like walls, with insignificant talus heaps at their bases, indicate a very recent origin. (A. L.)

PLATE XVIII

BACKGROUND.]

The vents on the plain to the south-east are not marked by craters or by fragmental materials, but by mounds of basalt less than fifty feet high spreading out into lava flows, which cover most of the surface near by. Here the eruptions seem to have consisted in a much quieter extrusion of lava alone. The basalts are all vesicular and very commonly quite light and cellular. (A. L.)

The basalts of the Benue plain likewise form low hillocks or mounds with no tuff or fragmental material to be seen. Generally there is no lava flow proceeding from them, and the extrusion of quite a small quantity of lava seems to have sufficed to relieve the pressure. Kaddemi Hill is an exception; an old basalt flow leads from it for two to three miles to the south-east. (A. L.)

All the basalt flows around Awe are raised considerably above the level of the plain, and protect the limestone shales below from denudation, though elsewhere the shales are very badly exposed. In consequence the flows rest on “pedestals” from thirty to fifty feet in height. Assuming that the lava chose the level surface of the plain rather than ridges upon it, it follows that since the eruptions around Awe there has been a general lowering of the surface by that amount. From this it appears that the Awe eruptions were not quite contemporaneous with those of Mboi, for at the latter place only a small amount of talus has been broken off from the crater cliffs. (A. L.)

The ash cones and puys of the middle Benue are much more imperfectly preserved than those of Kereng or Mboi and are certainly considerably older. Their comparatively recent age is presumed, however, as in the case of the later volcanic period in Air and Tibesti,[181] from the presence of thermal springs in the immediate neighbourhood. It seems probable that they were established as the result of the crustal movements anterior to the accumulation of the drift, while the puys of Kereng and Mboi owe their origin to the differential movements of the latest period of elevation.

In petrographical character these later rocks are very similar to the earlier Tertiary lavas. All are basalts rich in olivine and augite and varying in the same locality from types with abundant felspar in the ground-mass to thoroughly limburgitic[182] varieties (12) from which felspar is entirely wanting. The ash of the Kereng puy is remarkable for the number and size of the rounded augite crystals and olivine nodules which it contains. Recent flows of olivine basalt and limburgite are known also from Ahaggar and Air[183] and from the Kameruns.[184] M. Chudeau[185] has described rhyolites from Inzize to which he assigns a later Tertiary age, Dr. Passarge[186] has noted a nepheline basalt from an isolated cone of recent origin in the Benue valley between Yola and Garua, and Dr. Esch[187] has described nephelinites and leucitites from the Kamerun Mt. which is still periodically in active eruption. No rocks of similar composition, however, have been recognised amongst the products of the most recent volcanic period within the Protectorate.

MM. Chudeau[188] and Chautard,[189] following M. Lacroix,[190] have suggested that the alkaline rocks of North Africa may be grouped into three petrographical provinces, a western province including the Azores, Canaries, Cape Verde and Senegal, a central province including Ahaggar, Inzize, Air, Zinder and Mounio, Chad and the Shari valley, the Kameruns, and Dahomey, and an eastern province including Abyssinia, Arabia and Somaliland. Upon this hypothesis the alkaline rocks of Northern Nigeria belong to and complete the central province of Lacroix, as extended by M. Chudeau. It is probable, however, that this central province includes intrusive and volcanic rocks of many different ages, and that alkaline types have been a characteristic product of differentiation from the earliest times to the present day, (p. 142). There is, moreover, every reason to believe that the progress of investigation will reveal many connecting links between the various provinces, which are themselves somewhat too extensive and comprehensive to warrant their recognition as such. A petrographical province in the stricter sense of the term may perhaps be set up to include the alkaline plutonic rocks of Bauchi province and their associated hypabyssal types, but there can be little doubt that the general alkaline character of the igneous rocks of northern Africa, to which Lacroix has given expression, may be quite sufficiently indicated by emphasising their natural classification within the Atlantic branch of igneous rocks.[191]

[Footnote 172: Chautard, _Bull. Soc. Geol. Fr._, 4th Series, VII., 1907, p. 427.]

[Footnote 173: These rocks present in microscopical structure a decided resemblance to the Carboniferous lavas of the Bathgate Hills (Falconer, _Trans. Roy. Soc. Edin._, Vol. XLV., 1906, p. 133) in Scotland. With the exception that the doleritic types are somewhat less weathered, the description and classification of the Bathgate rocks may be applied almost word for word to these Tertiary lavas of Nigeria. Doleritic rocks (Falconer, _op. cit._, Plate I., Fig. 2) with phenocrysts of augite and olivine, and more rarely of felspar are common on the Morrua plateau in eastern Nassarawa and along the base of the escarpment between Darroro and Assab (928, 1573, 1630). Felspar is abundant in the ground-mass and the augite occurs in granules, granulitic aggregates, small ophitic plates, or minute idiomorphic crystals between the felspars. The basalts of Zammagan (1578) and Buratai (1640) show a typical fluxional arrangement of the felspars (Falconer, _op. cit._, Pl. I., Fig. 3). The basalt of Kwoia (1654) exhibits an intimate mixture of felspar and augite in the ground-mass (Falconer, _op. cit._, Pl. I., Fig. 4). The basalt of Assab (934) contains scattered felspars with abundant minute granular aggregates of augite, while a similar rock from Buratai and Dukshi (1641) contains some residual brown glassy material and passes into limburgitic varieties with phenocrysts of augite and olivine in an ill-defined microlitic base.]

[Footnote 174: Chudeau, _Sah. Soud._, 1909, p. 258; Gentil, _Doc. Sc. Miss. Sah._, 1905, p. 726.]

[Footnote 175: Passarge, _Adamaua_, 1895, p. 374. See also Downes, _Geol. Rep. Yola-Cross River Boundary Commission_, 1910, p. 35.]

[Footnote 176: Gentil and Freydenberg, _Bull. Soc. Geol. Fr._, 4th Ser., VIII., 1908, p. 35; Lacoin, _C. Rd. Ac. Sc._, 22 June, 1903.]

[Footnote 177: Garde, _C. Rd. Ac. Sc._, 149, 5 July, 1909, p. 43.]

[Footnote 178: Passarge, _Adamaua_, 1895, pp. 363, 384.]

[Footnote 179: Chudeau, _Sah. Soud._, 1909, p. 266.]

[Footnote 180: Chudeau, _Sah. Soud._, 1909, p. 361.]

[Footnote 181: Chudeau, _Sah. Soud._, 1909, p. 264.]

[Footnote 182: _Cf._ Falconer, _Trans. Roy. Soc. Ed._, XLV., 1906, Pl. I, Fig. 6.]

[Footnote 183: Chudeau, _Sah. Soud._, 1909, p. 361.]

[Footnote 184: Esch, _Geologie von Kamerun_, p. 40.]

[Footnote 185: Chudeau, _op. cit._, p. 259.]

[Footnote 186: Passarge, _Adamaua_, 1895, p. 384.]

[Footnote 187: Esch, _Sitz. Ber. Ak. Wiss. Berlin_, 1901, p. 277.]

[Footnote 188: Chudeau, _op. cit._, p. 268.]

[Footnote 189: Chautard, _Bull. Soc. Geol. Fr._, 4th Ser., VII., 1907, p. 427.]

[Footnote 190: Lacroix, _C. Rd. Ac. Sc._, 24 May, 1899, p. 1353; 1905, 140, p. 22. _Nouv. Arch. Mus._, 4th Ser., IV., p. 156; V., p. 246.]

[Footnote 191: _Cf._ Prior, _Min. Mag._, 1903, XIII., p. 228; Harker, _Nat. Hist. of Igneous Rocks_, 1910, p. 91.]

APPENDIX I

MINERAL RESOURCES

Salt — Iron — Gold — Monazite — Galena — Tinstone.

Detailed information respecting the principal mineral resources of Northern Nigeria will be found in Professor Dunstan’s Reports on the Results of the Mineral Survey.[192] The following is a brief summary of the more important facts.

(1). _Salt._

Salt has long been a staple article of inter-tribal commerce on the middle Benue, and its manufacture has in the past been extensively carried on in the province of Muri. The introduction of European salt has, however, adversely affected the native industry, and salt-making is now confined only to those localities in which the natural conditions are most favourable. In Muri province the salt is prepared by the concentration and evaporation of the waters of weak brine springs which are distributed over a western and an eastern area. In the western area the town of Awe is the centre of the industry, while Akiri and Azara are subordinate in both production and population. (Plate XVIII, Figs. 1, 2.) Keana on the Nassarawa border forms the western limit of the salt- producing area, while Akwana to the south of the Benue marks its southernmost extension. In addition to these towns which still manufacture a surplus for export, salt-making for local purposes is carried on at Kanji, Doya, Abuni, Ribi and Arofu within the same area. At a former period also salt was made at Lafin Gisheri, between Tunga and Ibi, and this locality may be taken to mark the eastern limit of the salt area. In eastern Muri the salt-producing district is of less importance than that in the west. The centres of the industry are Bomanda and Jenoe, but small quantities of salt are also prepared at Jebjeb, Jebero and Langa.

With regard to geological occurrence it is believed, as already indicated, that the weak brine from which the salt is made in Muri province is located within the upper part of the “Muri sandstones” and immediately underneath the passage beds and the Turonian limestone. Mr. Longbottom found that at Awe the springs supplied from the sandstones of the passage beds are entirely free from salt and cease flowing before the end of the dry season, while the neighbouring brine springs which rise from rocks lying below the surface drainage maintain a constant flow throughout the year. Moreover, wherever the shaly bands within the passage beds were pierced by boreholes, the brine rose with a steady flow under considerable pressure. The sandstones and grits underneath the passage beds appear to be saturated with weak brine which is retained, as in a reservoir, by the overlying shales. It is believed that the western and eastern salt-bearing districts form detached and irregular synclinal areas affected by a subordinate folding. The brine springs at Awe, Azara and Bomanda are especially associated with the subordinate anticlinal axes along which the salt-bearing beds within the synclinals approach the surface. Some of the minor salt towns, such as Ribi, Keana and Jenoe, are probably located on or near the outcrop of the salt-bearing beds. Wherever the brine springs are found, bubbles of a colourless gas, probably carbon dioxide, rise with the water. Calcareous incrustations round the orifices of the springs are found at Awe and Jebero. Some of the springs of Awe are, moreover, slightly thermal and possess a temperature a few degrees above sun heat. This is probably to be correlated with the recent volcanic action in the neighbourhood.

Distribution of Salt, Tinstone, Gold and Galena.

MAP No. 4.

London. Macmillan & Co., Ltd.

_Face p._ 266.]

The present springs rise in stream courses and are unavailable during the rainy season. Boring, however, within the synclinal areas would afford a copious and continuous supply. Professor Dunstan has analysed the salt of various localities and discussed the possibilities of increasing the native output. The general weakness of the brine, however, would appear to be unfavourable to European exploitation.

Salt is won from brine pools in south-eastern Bauchi over an extensive belt of country which stretches northward from the Pero Hills and passes to the east of Chongwom and Tangalto. The pools are presumably fed by springs and the salt is said to be abundant and easily prepared. The whole area, however, is very imperfectly known and largely unexplored. Scanty incrustations of natron, utilised by the local herdsmen, are known from the Gongola valley in the neighbourhood of Nafada.

In Bornu salt is made from the ash of the siwak tree (_Salvadora persica_) which grows abundantly on the ancient dunes which fringe the western shore of Chad. The slaves of Mongonu and Musara prepare salt also from the ash of three varieties of grass, “pagam, kalaslim and kanido,” which are found in the immediate neighbourhood of the lake. Over the whole of central Bornu the waters of the wells are charged with salts of soda in very varying amount. The ancient alluvium of Bornu is evidently impregnated with soda, and incrustations are found in places upon the surface of desiccated swamps. Natron pools, similar to those of Manga and presumably fed by springs, are unknown in central Bornu.

In Sokoto province incrustations of salt are found in the dry season at Zauro in the valley of the Gulbin Kebbi, and natron (kungwa) occurs in a similar manner between Gulma and Argungu. Knots and streaks of gypsum are common in the shales and clays around Sokoto, while efflorescences of gypsum and alum are found on the cliffs of Wurnu to the north-east. Scanty incrustations of natron are found upon desiccated swamps in many localities in the provinces of Sokoto, Kano, Zaria and Ilorin, but never in sufficient quantity to give rise to even a native industry. Hausaland has been in the past supplied with salt and natron from Asben, Bilma and Manga in the French Sudan. European salt, however, is rapidly replacing the native article, and many caravans now bring only natron from the north to the markets of Kano.

(2). _Iron._

As in the case of salt, so in the case of iron, the native manufacture has been very largely superseded by the importation of European bar- iron. Only in the more inaccessible districts or in those places where the ore is abundant do the natives still smelt the local ironstones in their primitive fashion. The surface ironstones were at one time generally utilised throughout the Protectorate as a source of iron. The magnetite sands are still washed and smelted by the pagans of the Mumuye hills in eastern Muri, while in northern Nassarawa the Koro tribe around Kao is still noted for its proficiency in the manufacture of iron from the local limonitic ores which occur within the schists in veins of varying thickness.[193] Similar ores occur in veins in the sandstones around Akiri in western Muri, but are no longer utilised by the natives. The oolitic and earthy ironstones of sedimentary origin and of Eocene age give rise to an extensive native industry around Akwi and Ojerami in central Kabba, around Mahorro in eastern Kontagora, around Aliero in southern Sokoto, and around Kantana in southern Bauchi, as well as in the Kerri Kerri country in western Bornu and in the Tagum hills in southern Bornu. So far as European exploitation is concerned, the sedimentary ores of Mt. Patti and the lower Niger are most favourably situated for transport. The ores, however, while abundant, are of a somewhat low grade character and relatively rich in phosphoric acid. Magnetite and hæmatite schists are extensively developed in eastern Kabba, but their composition would render necessary costly crushing and separating processes before the ores could be available for export.[194]

(3). _Gold._

Traces of gold have been found in some of the quartz veins which are so widely distributed throughout the Protectorate, but no payable reefs have yet been discovered. Small quantities of free gold occur in the streams between Koriga and Birnin Gwari in northern Zaria and around Tagum in southern Muri. In Zaria the gold is evidently located within the northern prolongation of the Zungeru belt of slates and schists, and further exploration may possibly lead to valuable discoveries. All the slaty belts already described within the Protectorate are, indeed, worthy of careful prospecting for gold. Small quantities of gold are also found associated with cassiterite in some parts of Bauchi province.

(4). _Monazite._

Monazite is widely distributed throughout the Protectorate, and appears to be a fairly constant constituent of the gneisses and schist. Small quantities are contained in almost every river and stream within the crystalline areas. It has been found most abundantly in central Kabba and in northern Nassarawa, but, so far as known, it occurs nowhere in sufficient quantity to afford any hope of profitable European exploitation.

(5). _Galena._

A slightly argentiferous galena occurs in veins within the Cretaceous rocks around Arofu and Akwana in western Muri, and in the Kudu valley to the west of Jebjeb in northern Muri. In the Arofu district the galena is associated with fluorspar and calcite, and the formation of the veins has been accompanied as already described by much silicification of the adjoining limestones. The Arofu galena is excavated by the natives for use as a cosmetic, and from time to time small pockets of silver are discovered within the veinstuff. To the west of Jebjeb the galena is no longer dug by the natives, and the old workings are now levelled and grassed over. The galena appears to have been associated with quartz, hæmatite and blende, but there is no evidence of silicification of the country rock.

(6). _Cassiterite (Tinstone)._

Tinstone is the most valuable asset of the Protectorate from the point of view of mineral resources. Its occurrence in western Bauchi was known to the natives long before the advent of Europeans. Recent investigation, however, by the Mineral Survey has proved its presence over considerable areas in widely separated localities within the Protectorate. The most extensive area over which tinstone is found in the surface alluvium occurs in western Bauchi, and includes the summit of the plateau and the greater part of its northern margin. The alluvial deposits of Naraguta, which lie within this area, were originally developed by the Niger Co., but have now been acquired by the Consolidated Gold Fields, Ltd. Elsewhere, however, tinstone becomes equally abundant, and there is little doubt that further investigation will reveal many localities within this extensive area in which alluvial workings may be profitably carried on. Several syndicates indeed are now engaged in exploiting certain portions of the tinfield. In the neighbourhood of Ngell the tinstone, accompanied by sulphide ores of copper, zinc and lead, occurs, as already described, in part as a pneumatolytic modification of the Bukuru granite, and in part as a true lode or pegmatitic formation. This particular occurrence is being developed by the Niger Co., but there is every reason to believe that similar occurrences will be found throughout the area as investigation proceeds.

Apart from this extensive tin-field in the centre of the Protectorate, cassiterite is also found in Bauchi province in many places throughout the Ningi and Burra hills, and detailed prospecting will probably here also reveal several payable localities. The completion of the Baro-Kano railway[195] within the next two years will afford an easy means of access to the tin-producing areas of Bauchi, and will at the same time largely overcome the difficulty of transport which is at present the greatest obstacle in the way of the development of the tin fields.

Beyond the limits of Bauchi province small quantities of tinstone have been found in the neighbourhood of Gadama and Fagam on the borders of Bauchi and Kano, around Gantam and Aribi on the Nassarawa tableland as well as on the eastern slopes of the Vere hills in Yola, the western slopes of the Shebshi hills in southern Muri, and in the neighbourhood of Eri in eastern Ilorin. In the latter locality the tinstone was found to be derived from a richly stanniferous pegmatite vein, but the actual extent and possibilities of the occurrence are as yet unknown. The same may be said also of the other localities indicated, and there can be little doubt that all of them are worthy of further investigation. Tinstone has been reported to occur abundantly in the Mada country in eastern Nassarawa, but this discovery likewise awaits confirmation.

[Footnote 192: Dunstan, _Col. Reps._ (_Miscell._), Nos. 32 (1906), 46 (1908), 47 (1908). A fourth report on the results of the Mineral Survey will shortly be issued.]

[Footnote 193: Sir William Wallace has reported an extensive native iron industry at Fawa in Katsina, where the ore appears to occur in a similar manner to that in the neighbourhood of Kao.—_G. J._, VIII., 1896.]

[Footnote 194: In _The Iron Ore Resources of the World_, Vol. II., 1910, p. 1029, Dr. J. W. Evans has given a _résumé_ of the results of the investigations of the Mineral Survey into the extent and value of the ferruginous deposits of Northern Nigeria.]

[Footnote 195: And the branch line to Leri in Zaria province.]

APPENDIX II

THE PALÆONTOLOGY OF THE UPPER CRETACEOUS DEPOSITS OF NORTHERN NIGERIA

By HENRY WOODS, M.A., _University Lecturer in Palæozoology, Cambridge_

The fossils collected by Dr. J. D. Falconer and Mr. A. Longbottom from the Upper Cretaceous deposits of Northern Nigeria include Fishes, Ammonites, Gasteropods, and Lamellibranchs. The localities from which these fossils were obtained are: Awe, Deba Habe, Jibaru, Gongila,[196] Gulani, Kumberi, Kunini, and Reme. At present the number of species which can be identified is comparatively small, but the collection is sufficient to show that under more favourable conditions a large and important fauna could probably be obtained from the deposits of this region.

Teeth, vertebræ, &c., of fishes were collected at Kumberi and Jibaru, and have been examined by Dr. A. S. Woodward who identifies them as _Gigantichthys_, a genus which is known from the Chalk of Egypt and the Sahara.[197] Ammonites have been found at Gongila, Reme, Kunini, and Kumberi, and they show that the deposits are of Turonian age—probably Lower Turonian. The Ammonites belong to the genera _Vascoceras_, _Mammites_ (_Pseudaspidoceras_), and _Hoplitoides_. _Vascoceras_ is confined to the Turonian. _Pseudaspidoceras_ is mainly of Turonian age. The species of _Hoplitoides_ belongs to the section of that genus which occurs in Turonian deposits. The species of _Vascoceras_ and _Mammites_ (_Pseudaspidoceras_) found in Nigeria are closely allied to forms which occur in the Lower Turonian of Northern Africa and the Iberian peninsula.

The larger number of the Gasteropods and Lamellibranchs were found at Awe, but no Ammonites were obtained at that locality; these fossils, so far as they can be identified, do not give any definite evidence that the deposit at Awe is of earlier age than the Turonian.

At Deba Habe _Ostrea (Exogyra) olisiponensis_, Sharpe, is abundant and is the only fossil obtained at that place. In Portugal that species occurs in both Turonian and Cenomanian deposits. In Nigeria it has also been found at Gongila, where the Turonian _Hoplitoides_ occurs. So that it is probable that the deposit at Deba Habe is of the same age as the one at Gongila.

At Gulani _Ostrea prælonga_, Sharpe, is abundant, but no other fossil was found at that locality. In Portugal _O. prælonga_ occurs in the Bellasian—an horizon which is believed to come between the Aptian and the Cenomanian. The same species is found at a similar level in Tunis and Algeria. The occurrence of this one species can, I think, hardly be taken as sufficient evidence that the deposit at Gulani is of Bellasian age, since it is not unlikely that, as is the case with _O. (Exogyra) olisiponensis_, this form may recur at later horizons when a favourable facies of deposit again appears.

At present, then, we can state that the deposits in which Ammonites occur are of Turonian age, and that there is not sufficient evidence to show that beds of earlier age are represented.

The fauna of the Turonian deposits of Northern Nigeria resembles closely that found in beds of similar age in Portugal, Tunis, and Algeria. This is shown especially by the Ammonites and oysters. At present the genus _Vascoceras_ is known only from Portugal, Spain, Algeria, Tunis, Egypt, Nigeria and Brazil. _Hoplitoides_ occurs in Algeria, Tunis, Nigeria, the Kameruns, and probably in Egypt. The species of _Pseudaspidoceras_ found in Nigeria is allied to forms found in Portugal, Tunis and Brazil. The oysters likewise belong to species characteristic of Northern Africa and South-western Europe, and one of them has also been found as far south as Angola. The Ammonites also show, as Pervinquière has already pointed out is the case in Tunis, that the fauna is related to that found in the Upper Cretaceous of Brazil.

Amongst other places in West Africa, Cretaceous deposits have been found in the Kameruns, and are regarded by Solger as of Upper Turonian and Lower Senonian age, but by Harbort[198] they are referred to the Emscherian (Lower Senonian). They certainly appear to be of later date than the Nigerian deposits with which they are connected chiefly by the presence of _Hoplitoides_.

Until the fauna of the Nigerian Cretaceous is more completely known any further discussion of its relationship to the faunas of other areas must be postponed.

The list on the following page shows the distribution of the species found in Nigeria, and is followed by palæontological notes and descriptions of some of the species.

--------------------+----+-----+--------+-------+--------+-------+----- |Awe.|Deba |Gongila.|Gulani.|Kumberi.|Kunini.|Reme. | |Habe.| | | | | --------------------+----+-----+--------+-------+--------+-------+----- _Nuculana_, sp. | | | | | * | | | | | | | | | _Trigonoarca_, sp. | * | | | | | | | | | | | | | _Trigonia_, sp. | * | | | | | | | | | | | | | _Modiola_, sp. | * | | | | | | | | | | | | | _Pecten (Neithea) | * | | | | | | quinquecostatus_, | | | | | | | Sow. | | | | | | | | | | | | | | _Lima (Mantellum)_, | * | | | | | | sp. | | | | | | | | | | | | | | _Ostrea prælonga_, | | | | * | | | Sharpe | | | | | | | | | | | | | | „ _(Exogyra) | | * | * | | | | olisiponensis_, | | | | | | | Sharpe | | | | | | | | | | | | | | _Gervillia | * | | | | | | (Pseudoptera)_, sp. | | | | | | | | | | | | | | _Astarte awensis_, | * | | | | | | sp. nov. | | | | | | | | | | | | | | _Lucina_, sp. | | | | | * | | | | | | | | | _Cardium_, sp. | * | | | | | | | | | | | | | _Corbula_, sp. | * | | | | | | | | | | | | | _Pseudomelania_, sp.| * | | | | | | | | | | | | | _Turritella_, sp. | | | | | * | | | | | | | | | _Semifusus | * | | | | | | africanus_, sp. nov.| | | | | | | | | | | | | | _Vascoceras | | | | | | * | * nigeriensis_, sp. | | | | | | | nov. | | | | | | | | | | | | | | „ | | | * | | | | _gongilensis_, sp. | | | | | | | nov. | | | | | | | | | | | | | | _Mammites | | | * | | | | (Pseudaspidoceras)_,| | | | | | | sp. | | | | | | | | | | | | | | _Hoplitoides | | | * | | | | nigeriensis_, sp. | | | | | | | nov. | | | | | | | | | | | | | | „ sp. | | | | | | | * | | | | | | | _Gigantichthys_, sp.| | | | | * | | --------------------+----+-----+--------+-------+--------+-------+-----

LAMELLIBRANCHIA.

NUCULANA, sp.

Plate XIX., Fig. 4.

An internal cast resembles in form _N. Mariæ_ (d’Orbigny), but in the absence of the shell the species cannot be identified.

_Locality._—Kumberi.

TRIGONOARCA, sp.

Plate XIX., Figs. 1–3.

Several specimens of _Trigonoarca_ were found, but are not sufficiently well-preserved for specific identification. In general form they resemble some examples of _T. trichinopolitensis_ (Forbes)[199] from the Trichinopoli Beds of Southern India.

_Locality._—Awe.

TRIGONIA, sp.

Two specimens of a species belonging to the Scabræ section of _Trigonia_ are in the collection, but are not sufficiently well-preserved for identification.

_Locality._—Awe.

MODIOLA, sp.

Examples of a small form of _Modiola_ occur at Awe.

PECTEN (NEITHEA) QUINQUECOSTATUS, Sowerby.

Three specimens with the shell preserved were found at Awe.

LIMA (MANTELLUM), sp.

An imperfect specimen from Awe resembles _Lima (Mantellum) gaultina_, Woods.[200]

OSTREA PRÆLONGA, Sharpe.

Plate XIX., Figs. 5–8.

1850. _Ostræa prælonga_, D. Sharpe, _Quart. Journ. Geol. Soc._, VI., p. 187, Pl. XX., Fig. 4.

1869. _Ostrea prælonga_, H. Coquand, _Mon. Ostrea. Terr. Crét._, p. 169, Pl. LXVI., Figs. 1, 2.

1890. _Ostrea prælonga_, A. Peron, _Moll. Foss. Terr. Crét. Tunisie_, p. 110, Pl. XXIII., Figs. 1–6.

_Remarks._—About twenty more or less perfect specimens of an _Ostrea_, agreeing closely with _O. prælonga_, Sharpe, were found. _O. pentagruelis_, Coquand,[201] is considered by Peron to be only a very old individual of _O. prælonga_.

This species occurs in the Bellasian of Portugal. In Algeria and Tunis it is characteristic of beds which occur below the Cenomanian, and are referred by Peron to the Upper Albian.

_Locality._—Gulani.

OSTREA (EXOGYRA) OLISIPONENSIS, Sharpe.

Plate XX., Figs. 1–3.

1850. _Exogyra olisiponensis_, D. Sharpe, _Quart. Journ. Geol. Soc._, VI., p. 185, Pl. XIX., Figs. 1, 2.

1862. _Ostrea Overwegi_, H. Coquand, _Géol. pal. rég. sud. prov. Constantine_, p. 226, Pl. XIX., Figs. 1–6.

1862. _Ostrea Coquandi_, Julien, in Coquand, _ibid._, p. 324, Pl. XXXIII., Figs. 10–12.

1869. _Ostrea olisiponensis_, H. Coquand, _Mon. Ostrea. Terr. Crét._, p. 125, Pl. XLV., Figs. 1–7.

1869. _Ostrea Overwegi_, Coquand, _ibid._, p. 140, Pl. XLIV., Figs. 1–9; Pl. XLVI., Figs. 14, 15.

1873. _Ostrea olisiponensis_, L. Lartet, _Ann. Sci. géol._, Vol. III., p. 59, Pl. XI., Fig. 1.

1882. _Exogyra olisiponensis_, G. Seguenza, _Atti d. R. Accad. dei Lincei_, Ser. 3; _Mem. Scien. Fis. Math._, Vol. XII., p. 180, Pl. XVII., Fig. 2.

1882. _Exogyra oxyntas_, Seguenza, _ibid._, p. 178, Pl. XVIII., Fig. 1.

1888. _Ostrea olisiponensis_, P. Choffat, _Mém. Soc. Phys. et d’hist. nat. de Genève_, XXX., 2, p. 95.

1891. _Ostrea olisiponensis_, A. Peron, _Moll. Foss. Terr. Crét. Tunisie_, p. 114, Pl. XXIII., Figs. 14–18.

1902. _Ostrea (Exogyra) olisiponensis_, P. Choffat, _Faune Crét. Portugal_, Vol. I., Ser. 4, p. 166, Pl. VI., Figs. 17–19.

1903. _Ostrea olisiponensis_, R. Fortau, _Bull. Instit. Égypt._, Ser. 4,