Chapter IV: Cretaceous Rocks

Distribution: relation to crystalline rocks. The Cretaceous rocks of the Benue valley: the succession around Awe; the position of the salt- bearing beds; the Arofu and Akwana limestones and galena veins; the limestone-shales and brine springs of eastern Muri; the Muri sandstones; the Gateri grits; the limestones and galena veins of the Kudu valley. The Cretaceous rocks of Yola and of the Gongola valley: the Bima sandstones; the Gongila limestone; the rocks of Gulani and Wuyo; the upper sandstones of Ture and Waja. Classification of the Cretaceous rocks. The Cretaceous rocks of the French Sudan, Southern Nigeria and the Kameruns.

No rocks of Devonian or Carboniferous age or of any period preceding the Cretaceous[70] have been discovered within the Protectorate. The Cretaceous rocks, moreover, are themselves represented only by the upper members of the series, no deposits of earlier age than the Turonian having been anywhere definitely recognised. The Upper Cretaceous rocks are confined within the Protectorate to the Benue valley between long. 8°·30′ E. and long. 12°·15′ E., and to the valley of the Gongola between its confluence with the Benue and lat. 11°·15′ N. They form the greater part of the plains of Muri and Yola, and of the narrow plain of the Gongola in Bauchi and Bornu, but only around Ligri and Gateri and in Wurkum, Tangale and Waja do they rise into ranges of rounded or tabular hills. The rocks consist of a well-bedded series of red and white sandstones and grits, carbonaceous and calcareous shales, ironstones and limestones, usually somewhat faulted and gently folded into low anticlines and shallow synclines, and in places pierced by intrusive masses of dolerite or basalt. The original thickness is unascertainable, partly on account of the folding and faulting to which the rocks have been subjected and partly on account of the thick covering of drift which obscures the rocks for long distances and renders difficult or impossible the correlation of the various exposures. In the west the Cretaceous rocks are believed to pass unconformably under the sandstones of the Lokoja series in the neighbourhood of Udeni, but the actual junction has nowhere been observed. How far westward they extend under the Lokoja sandstones is also undetermined. An exposure of white sandstones and carbonaceous shales in the bed of a stream near Akwacha in Bassa province seems to indicate that they extend for a considerable distance west of Loko, but that they do not reach the Niger is abundantly evident from the absence of any trace of them in the neighbourhood of the river below Lokoja.

To the north and to the south of the plains of Muri, the Cretaceous sandstones give place imperceptibly to a crystalline floor. The actual contact, however, has been found wherever examined to be so much obscured by drift that it is impossible to say whether any part of the margin is bounded by faults or not. In the east the Cretaceous rocks pass under the upper Benue sandstones and, so far as known, do not reappear anywhere east of Yola. Similarly in the Kudu valley they disappear under the sandstones of Duguri and in the Gongola valley under the Gombe sandstones to the west and north. To the east of the Gongola between Bilaraba and Dusua they rest upon a hummocky crystalline surface, while farther south they pass behind Balbea under the Barbur basalt plateau. To the west of Kwoia, however, their junction with the crystalline rocks, although somewhat badly exposed, has every appearance of being fractured, while on the lower Gongola the relations between the Cretaceous and the crystalline rocks to the east are such as to suggest most forcibly an extensive faulting along the contact. Within the area covered by the Cretaceous rocks inliers of granite and gneiss are exposed around Arofu on the middle Benue, around Tangalto and Chongwom in southern Bauchi and in various places upon the narrow plain of the Gongola and, while in some cases the crystalline rocks exposed upon the plain of the Gongola have undoubtedly been brought to the surface by faulting, it is at the same time fairly certain that the earlier Cretaceous rocks were deposited upon a highly irregular crystalline floor, the more elevated portions of which have been exposed at the surface in the course of denudation. For the same reason also the apparent base of the Cretaceous in the neighbourhood of these inliers of crystalline rock cannot be regarded as the actual base of the series, which is at most very imperfectly known.

_Muri Province._

In Muri province a series of limestones and shales definitely known to be of Upper Cretaceous and Turonian age[71] is exposed in western Muri around Awe to the north and around Arofu and Akwana to the south of the Benue. In eastern Muri, the same series is found at Kumberi on the right bank of the Benue a few miles above Amar. At Awe a sharp little anticline runs E.N.E. along the north side of the town and brings up coarse white felspathic grits and sandstones with two bands of carbonaceous shales (Plate XV, Fig. 1). It begins to the north-east of the town as a gentle arch with its axis dipping gently westward. The intensity of the folding increases rapidly in that direction until the anticline passes into a fault with the downthrow towards the north, but farther west the fold reappears and speedily flattens out. The northern limb of the fold is much more steeply inclined than the southern and the beds are even in some places overturned. At the same time the sandstone outcrop takes the form of a bow with the concave side to the north, the whole structure being evidently produced by a local intensification of the folding. (A. L.)

To the north and south of Awe, there are synclinal areas in which rocks higher in the series have been preserved. From the various exposures in the neighbourhood the following approximate sequence can be made out:

Soft white quartzose sandstones, often with calcareous cement.

Thinly-bedded light-coloured calcareous shales and sandstones with bands of impure shelly limestone.

Greenish shales with ironstone bands and nodules.

White grits and sandstones and carbonaceous shales with brine springs.

Base not exposed.

(A. L.)

Grits and sandstones similar to the lowest beds seen at Awe, with brine springs but without carbonaceous shales, come up to the surface again along a line running from Akiri to Azara and Ribi, but north of that again comes another synclinal area, for between Azara and the Ankwe river exposures of shales and limestones are met with. Over the whole of this part of Muri indeed the beds appear to be thrown into gentle anticlines and synclines whose axes run approximately E.N.E. A lower and essentially sandy division, often yielding brine, appears along the cores of the anticlines as at Azara, Akiri and Awe, while an upper, essentially shaly division, is preserved in the intervening synclinal areas. (A. L.)

Limestones are known to occur in the volcanic tract on the Benue, south- west of Awe, while at Tunga wharf, immediately south of Awe, a river section exposes the lower sandstones striking E.N.E., and dipping northwards at 27°. At Arofu a small inlier of granite to the east of the town is seen to be five-sixths surrounded by silicified limestone with the remainder of its perimeter concealed by marshy ground. An excavation proved the limestone to rest directly on the granite and we are therefore compelled to conclude that this granite forms a knoll surrounded and at one time overlaid by the limestone. Whether similar relations hold good between the other inliers of crystalline rocks in the neighbourhood and the limestone is not certain. The outcrop of the limestones is a broad one, about half a mile across in the vicinity of Arofu and still more to the south of Akwana. The broad outcrop is accounted for partly by the gentle dip, partly perhaps by gentle undulations of the strata, but partly also by the thickness of the limestone. What this is it is impossible to say in the present state of our knowledge, but it is certainly much greater than that of the limestone bands known in the neighbouring parts of the province. (A. L.)

The saltings of Arofu and Akwana bear witness to a salt-bearing series underneath the limestones although that series itself is nowhere exposed. Above the limestones comes a series of shales, shaly sandstones and ironstones with a few thin intercalated limestone bands. This shaly series outcrops between Arofu and the river and runs a little south of west to beyond Akwana. The dip is about 10° and almost north. At Shaii however, twelve miles east of Arofu, similar shales dip at 25° towards N. 40° E., so that the folding is somewhat variable. Around Arofu the limestones are seldom seen in an unaltered condition, for almost all the rock exposed is silicified. Thus the country is crossed by innumerable dyke-like masses of silicified limestone standing up several feet above the soil. In the rising ground south of Akwana the silicified bands give rise to several small cascades. Knots of galena are common in the silicified limestone and in places as at Arofu there are veins of galena and fluorspar. The original structures of the limestone which was partly foraminiferal but very largely oolitic and pisolitic have been excellently preserved during the change. At Arofu, however, a compact unaltered variety contains imperfect remains of ammonites. It is possible that these limestones which lie to the south of the Benue may be on a somewhat different horizon from those of Awe, but the presence of the underlying salt-bearing series indicates that the general succession is the same. (A. L.)

At Kumberi some miles above Amar there occurs the following excellent riverside section of the limestone-shale series, in which the subordinate character of the limestone bands is very evident:

Occasional sandstone seen in the river bank:—

About 100 ft.—Fine-grained sandstone, mudstone and shales alternating
as below.

12 „ Sandstone.

About 50 „ Shales.

2 „ Good white limestone with numerous teeth, bones, and
phosphatic casts of lamellibranch and gasteropod shells.
Ammonites.

6 „ Shales.

1½ „ Shelly limestone.

8 „ Shales.

2 „ Friable sandstone.

10 „ Shales with mudstone bands.

15 „ Blue-gray shales.

20 „ Shales with mudstone bands.

2 „ Mudstone with large calcareous concretions round
ammonite shells.

5 „ Shaly sandstone.

10 „ Friable sandstone.

2 „ Sandy shales.

10 „ Soft, friable sandstones with shaly partings.

About 200 „ Fine-grained and soft sandstones, mudstones, and shales
alternating as above.

Occasional sandstones in river bank.

Total: 450 to 500 ft. Limestone : 3½ ft.

Strike uniformly N. 50° E.; dip, 30°–35° S.E.

(A. L.)

Farther east again scattered fragments of limestone indicate the presence of the limestone-shale series in a synclinal between Bomanda and Muri. An anticlinal axis, running a few hundred yards south of Bomanda, brings up a lower series of soft thinly-bedded calcareous grits with partings of green calcareous marl along the crest of the arch. Brine springs like those of Awe rise through the northern limb. At Muri the lower reddish grits are seen in full force and dip southwards at about 60°. A careful estimate of the thickness exposed worked out at over 1,500 ft. though neither the base nor the upper limit was seen. To the north fragments of limestone are found in the swamps of the Kudu valley to the west of Jebjeb and Gateri but the associated rocks have nowhere been observed. (A. L.)

The white grits and sandstones and carbonaceous shales of Awe and the calcareous grits and marls of Bomanda represent the passage beds between the upper limestone-shale series and the lower sandstones exposed at Akiri, Ribi and Tunga wharf in the west and at Muri town in the east of the province. The weak brine which rises in springs through the passage beds at Awe and Bomanda and even through the limestones at Akwana appears to take its origin in the upper part of the lower sandstone series. Brine springs and surface incrustations are found also where the lower sandstones outcrop at Jebjeb, Jebero, Jenoe, and Langa in eastern Muri, at Akiri, Azara, Ribi, Kanje and Abune in western Muri, and at Doya and Keana on the borders of Nassarawa. These localities occur immediately round the margins of the more marked synclinal areas containing the remains of the limestone-shale series, a fact which warrants the assumption that the upper part of the sandstones underlying the limestones is impregnated with salt and was originally accumulated under arid conditions. Indications of the salt-bearing strata are also found at Lafin Gisheri between Tunga and Ibi and at a place of the same name between Shishi and Wurio to the east of Ibi. In these localities we are justified in assuming that the rocks immediately below the surface belong also to the upper part of the lower sandstone series.

To the north of the salt area in western Muri well bedded sandstones are exposed in many places between Lafia in Nassarawa province, and Wase and Bashar to the north of Ibi. The prevailing type of rock is a reddish grit or sandstone, frequently brick red, with knots and spots of white felspathic material, everywhere unfossiliferous, and nowhere yielding any indication of salt impregnations. At Bashar thin beds of white and red clay are interstratified with the sandstones. The rocks are usually inclined at a low angle to the horizontal and appear to be thrown into a series of gentle undulations. From their position with respect to the salt-bearing beds and the limestone-shale series, it may be assumed, although continuous exposures are wanting, that these rocks lie conformably at or near the base of the sedimentary succession in western Muri. Their thickness is unknown, but if, as seems probable, they are to be correlated with the sandstones of Muri town which underlie the limestones in the eastern part of the province, they must be, according to Mr. Longbottom’s determination (p. 151), at least 1,500 ft. thick, and they may well be more. The whole series underlying the passage beds of Awe and Bomanda and impregnated with salt in the upper part may conveniently be termed the “Muri sandstones.”

PLATE XI

Upon the drift-covered plains of southern Muri are found occasional detached exposures of sandstones and grits, the majority of which probably belong to the lower sandstone series. The presence of the “Muri sandstones” underneath the limestones of Arofu has not been demonstrated but, as already stated, the occurrence of brine springs at Akwana affords a considerable presumption in favour of their occurrence. Whether they outcrop in the unexplored Munchi country to the south and south-west of Akwana is, however, quite unknown.

In the north-eastern part of the province the “Muri sandstones” become more steeply folded, and in the Jenoe, Ligri, and Gateri hills appear to be underlaid by a series of very coarse-grained white felspathic grits or arkoses. The axes of the folds strike in a general way a few degrees north of east, and the folding appears to be most intense in the immediate neighbourhood of Gateri where the grits are much hardened, and in places set on end. On the western slopes of the Gateri hills are white and red grits and sandstones, the representatives of the “Muri sandstones,” dipping generally westward and apparently underlying the fragmentary limestones of the Kudu valley. In the Gateri hills, moreover, there are indications, as at Awe, that the axes of the folds are not horizontal, but tilted gently to the west, and the distribution of the upper limestones in Muri province in elliptical areas or irregular centroclinals surrounded by the lower sandstones clearly suggests a later transverse corrugation of the whole series of gently folded rocks. It is probable, therefore, that the limestones of the Kudu valley, although originally occupying a much higher place in the series than the Gateri grits, have reached their present relatively low position, not so much as the result of faulting, but rather as the result of the irregular folding to which the whole series has been subjected. At the same time the occurrence of galena veins in the swamps to the west of Jebjeb indicates that the rocks of the Kudu valley, like those of Awe and Arofu, have undergone a certain amount of shattering and fissuring contemporaneously with the folding. Amongst the fissure- veins may also be included the broad dykes of limonitic ironstone which form conspicuous hillocks around Akiri in western Muri.

_Yola Province._ (A. L.)

The limestone-shale series runs up the plain of the Benue from Lau almost to Yola, and may even be found eventually farther east than Yola. This series occupies the lower ground and nowhere forms hills. In addition to it there are sandstones of various kinds, sometimes occupying the plain and sometimes building up hills above the plain. The sandstones of the hills are approximately horizontal and rest upon the lime-stone-shale series. They will be referred to as the “Upper Benue sandstones.” The question of their conformability or otherwise to the limestone-shales will be discussed later (p. 188).

The limestone-shale series, being soft and easily denuded, is very poorly exposed, and is generally hidden by the river alluvium. Calcareous sandstone and greenish yellow shale are seen near Lau, and south-west of Kunini large blocks and slabs of shelly limestone a few inches thick lie scattered about over the silt. An excavation at Kunini proved that the limestone is in thin bands, 12 or 18 inches thick, intercalated between shales. The series is thrown into small anticlines and synclines. Of one small anticline noticed the strike of the axis was N. 10° E., one limb being inclined at 20°, the other at 60°. The shales are seldom seen but they give rise to a characteristic soil which is easily recognised and which leads to the discovery of limestone lumps and fragments on further search. Low-lying country of this character, with numerous slabs and lumps of limestone lying about on the surface stretches up the Benue to the vicinity of Namtari.

Similar areas of limestone-shales are found on the Gongola between Kiri and Shillen and between Mada and Kombo. The latter area runs up the plain of the Maio Hawal, but for what distance is unknown. In both areas the limestone is shelly and very fossiliferous and there are no sections showing the shales or giving the dips. The only natural section of this series which was met with in Yola province was at Numan. Just to the east of the village, white fine-grained sandstone crops out and is followed by still finer sandstones and mudstones on which the village itself is built. No limestone appears in the section and only a little shale. The dip is 10° towards N. 55° W. The mudstone is usually reddish, but the fresher parts are greenish and glauconitic-looking. Phosphatic nodules are found in this material and also in lumps of shelly limestone set up by the natives in Dong. A small inlier of Cretaceous limestone is exposed also between Jibaru and Murki in eastern Yola to the north of the Bagele hills.

The thick grits and sandstones which emerge from beneath the limestone- shale series in Muri province are probably responsible for the bold escarpment behind Wuduku, but in the absence of detailed examination it is impossible to say if these infra-limestone grits were ever deposited in Yola province, and if, being so deposited, they crop out between the limestone-shale series and the crystallines or are faulted out. The problem, a simple one in itself, is enormously complicated by the fact that the “Upper Benue Sandstones” rest upon the limestone-shales and conceal their boundary with the crystallines. Consequently, the relation of the Cretaceous rocks to the crystallines is at present unknown.

The Cretaceous rocks floor the trench of the upper Benue valley, while the plateau areas to the south and, east of the Gongola, to the north also, are of crystallines. It is improbable from the characters of the limestone-shale series that these beds were formed in a narrow inlet running up into a land mass. On the contrary they are fine-grained marine sediments which were probably deposited in open water. Their present position, on the floor of the valley, at a much lower altitude than the crystalline plateaux north and south must be explained as the result of tectonic movements. The wrinkled character of the series is consistent with this explanation, and in this connection sections in the neighbourhood of Kombo are suggestive. There the broad channel of the Gongola, usually half a mile wide, becomes suddenly constricted to less than a hundred yards by a ridge of grits dipping at 50° towards S. 30° E. These grits pass under limestone-shales to the south-east, and must therefore be correlated with the Awe and Bomanda grits. When followed eastward, however, for only a few miles, this prominent ridge of grits disappears, and the limestone-shales are seen to approach to within at least a few yards of the granite. This strongly suggests that the limestone-shale belt running up the Maio Hawal is faulted down to abut against the granite. In a similar way, it is believed that the Upper Benue valley, to the east of its confluence with the Gongola, was initiated as a tectonic valley. (A. L.)

_Bauchi and Bornu._

To the north as to the west of Gateri, a series of white sandstones intervenes between the Gateri grits and the limestones which outcrop in the swamps between Putu and Tangalto. These limestones are exposed in a very fragmentary manner, but the presence of a narrow belt of the lower white salt-bearing sandstones in the midst of the limestones half-way between Putu and Tangalto indicates here as elsewhere the occurrence of the usual succession and an irregular folding of the whole series. Approaching Tangalto the Cretaceous rocks run out upon the crystallines as white sandstones and quartzose conglomerates whose horizon probably coincides with those of the Ture grits to the east. In the hilly country to the east of Tangalto and on the plains to the north, the inclination of the Cretaceous rocks is in part due to a gentle folding, and in part to an extensive faulting which has in places on the Gongola plain brought up even the base of the series and the underlying crystalline rocks to the same level as the limestones. Around Ture (Plate XIII, Fig. 1) and Awok, the varied dip of the well-bedded sandstones indicates a gentle curving into low domes and shallow basins, while a similar structure is very evident at Gulani, to the east of the Gongola, where the town is set within a circle of low hills which possess a well-marked centroclinal dip. On the other hand, the Wadi, Shinga, Bima and Gunna hills, are separated by faults, and owe their greater northerly inclination to the effect of a larger fault which is well seen at Gunna on the left bank of the Gongola, and on the track between Wadi and Wuyo, where the basal sandstones of the Bima hills with the underlying crystalline rocks are brought up to the surface of the plain. The faulting, like the folding, appears to be in two well-marked directions at right angles to each other and approximately N.N.W., and E.N.E., and it is probable that there is here, as in the neighbourhood of Awe, some intimate relation between the faults and folds, for whose complete demonstration much more detailed investigation would be required.

If the Gunna fault be taken as showing the base of the Cretaceous, the succession in the Gongola valley begins with a series of sandstones and grits at least 1,000 ft. thick. The basal beds are green and purple earthy grits, composed of the debris of crystalline rocks and containing large rounded fragments of granite and pegmatite. These are followed by alternating bands of red, white and purple grits, which pass into the white and red sandstones and grits of the Bima and Wadi hills. The marginal rocks, which overlie the crystallines between Bilaraba and Dusua are white, red, and purple grits, much broken and current bedded and probably belonging to the same horizon as the lower sandstones of the Bima hills. These “Bima sandstones” are succeeded after an unknown interval by the Cretaceous limestones which outcrop in many places upon the plains to the east and to the west of the Gongola, and are particularly frequent over the tract of country which lies between Dukul and Deba Habe to the west, and Wuyo and Gulani to the east of the river. In one locality, a mile to the south of the village of Gongila, between Nafada and Ashaka, the limestone is clearly shown resting upon the lower series of white and red sandstones and grits. As a rule, however, the rocks associated with the limestone, are badly exposed and obscured by drift, while the shales which presumably accompany the limestones have nowhere been observed. At Gulani, the limestones pass conformably under a series of coarse white and red grits and white, yellow and brick red sandstones with intercalated bands of clay and flaggy ironstones. With these upper rocks the red and white sandstones, clays, and ironstones of Wuyo present much lithological resemblance and probably belong to the same horizon. Similarly at Reme in the extreme south-east of Bauchi province the limestones are overlaid by a well-stratified succession of white and red sandstones, grits, and flaggy ironstones, which are at least 800 ft. thick, and form the escarpments of the flat-topped hills of Waja. The whole series becomes markedly ferruginous towards the summit, and while the contact with the limestones below is not actually exposed, there is no reason to believe that it is other than conformable. These rocks in Waja represent the highest known members of the Cretaceous series, and it is they which are continued westward by Tula, Awok, and Ture, and run out upon the crystallines to the east of Chongwom. Around Awok and Ture these upper sandstones are distinctly and variously inclined, but in Tula and Waja the dips are so gentle as to be almost imperceptible. The white grits and sandstones are usually unfossiliferous, but in the neighbourhood of Ture and the Peak (Plate XIII, Fig. 2), they contain much silicified wood from the presence of which a subsidiary argument may perhaps be drawn in favour of their Cretaceous age. The Gongola valley to the east and north-east of Waja retains the faulted character which it exhibits to the north, while the country which lies between the escarpments of the Waja hills on the north, and the Yam Yam hills fronting the Benue on the south, is quite unknown and may contain representatives of both granitic and sedimentary rocks.

From the various exposures described, the Cretaceous series within the Protectorate may be tabulated as follows:

----------+-----------------------------+---------------------------
| Muri and Yola. | Bauchi and Bornu.
----------+-----------------------------+---------------------------
Upper | |Sandstones, grits, clays,
grits and | |and ironstones of Waja,
sandstones| |Ture, Gulani and Wuyo.
| |
Limestones| Turonian limestones and |Turonian limestones of the
| shales of the Benue valley |Gongola valley.
| |
|{ Passage beds (white |
|{ sandstone and carbonaceous |
|{ shales at Awe: calcareous |
Lower |{ grits and green calcareous |
grits and |{ marls at Bomanda). |
sandstones|{ |
|{ Muri sandstones (upper part|Bima sandstones and grits.
|{ salt-bearing). |
|{ |
|{ Gateri grits. |
----------+-----------------------------+---------------------------

No evidence of contemporaneous volcanic activity has been found within the Cretaceous rocks of the Protectorate. Intrusive sills of dolerite, however, have been observed within the Cretaceous sandstones in the neighbourhood of Awe, Bashar and Serakin Kudu in Muri province, but they, together with the numerous pipes and necks of basalt and trachyte which pierce the Cretaceous rocks in the valleys of the Benue and Gongola, are probably to be referred to some phase of Tertiary volcanic activity (see Chapter VIII).

In the French Sudan limestones of Turonian age have been described from the Damergou[72] to the north of Zinder, from Bilma to the north of Lake Chad,[73] and from Tabankort, Tabrichet and Mabrouka[74] to the south and west of the Adr’ar’ des Ifor’as. The occurrence in the Damergou of gypsiferous clays in association with Cretaceous limestones has not been paralleled in Northern Nigeria. On the other hand the presence of a salt-bearing series within the Cretaceous has not hitherto been recognised in the Sahara. Any correlation of the lower grits and sandstones of Northern Nigeria with the Lower Cretaceous of the Tegama, as established by M. Chudeau,[75] would, however, be premature, in view of the absence of determinative fossils in both and the marked lithological differences between the two. It seems better for the present to avoid any definite subdivision other than that indicated above and to refer the whole series of grits, sandstones, clays, ironstones and limestones provisionally to the Upper Cretaceous. To the south of the Protectorate rocks of a similar age have been described by Mr. Parkinson[76] and Dr. Esch[77] from Southern Nigeria and the Kameruns respectively.

[Footnote 70: See Chudeau, _Sah. Soud._, 1909, pp. 47, 11, for pre- Cretaceous rocks of the Sahara.]

[Footnote 71: See Appendix II, _Palæontology_, p. 273.]

[Footnote 72: De Lapparent, _C. Rd. Ac. Sc._, 135, 1903, p. 1298; Chudeau, _Sah. Soud._, 1909, p. 89.]

[Footnote 73: De Lapparent, _C. Rd. Ac. Sc._, 132, 1901, p. 388.]

[Footnote 74: Chudeau, _Sah. Soud._, 1909, p. 91.]

[Footnote 75: _Ibid._, p. 76.]

[Footnote 76: Parkinson, “The Geology of the Oban Hills,” _Q. J. G. S._, 63, 1907, p. 314.]

[Footnote 77: Esch, _Geologie von Kamerun_, 1904, p. 4.]