Reports and Proceedings — Geological Society of London. 327 



In the detailed succession now worked out, the Ashgillian and the 

 Valentian are for the first time distinguished, while the distinction 

 between the Wenlock and the Ludlow Beds is brought out by means 

 of graptolite zones. 



The stratigraphical succession is shown by traverses ; but, owing to 

 successive overlap of the upper beds, no single traverse gives the full 

 succession. The different groups are traced over the area mapped, 

 and the chief fossiliferous exposures described, with full lists of the 

 fossils obtained. The district is shown to be transitional in character 

 between neighbouring districts on almost every side, combining many 

 of their features. 



The structure of the area is mainly that of an anticline with 

 ' keystone ' faulting, the dominant features being determined by the 

 intrusive masses of the Breidden Hills and the small Standard Dyke 

 of Welshpool. The two boundary faults of the arch have very 

 considerable downthrows. 



A brief account is given of the Welshpool Dyke, with chemical 

 analyses of the rocks. 



The glacial geology of the area is also described, three series, of 

 deposits being observed : (1) a high-level series, (2) a low-level series, 

 and (3) a stratified series. The Guilsfield Valley is shown to have 

 been occupied by a glacial lake, and the reversed drainage of the 

 Cefn-Tspn Brook is shown to be connected with a ' col ' through 

 which the overflow water drained. 



A short description of some of the fossils, including one or two new 

 species, is given, and the paper is supplemented by correlation tables 

 and maps. 



2. Dr. J. D. Falconer, ]VT.A., F.G.S., then gave an account of the 

 Geology of Northern Nigeria, illustrating his remarks by means of 

 lantern-slides. He pointed out that the Protectorate of Northern 

 Nigeria covers an area of about 255,000 square miles, over half of 

 which crystalline rocks are exposed at the surface. A series of hard 

 banded gneisses of an Archaean type is intermingled with a series 

 of quartzites, phyllites, schists, and gneisses of sedimentary origin, 

 in such a way as to suggest that the two series, while originally 

 unconformable, have been at a later period affected by a common 

 folding and foliation along axes which are predominantly meridional 

 in direction. The two series have also been pierced by numerous 

 igneous intrusions of a granitic type, which are subdivided into (1) an 

 older, wholly or partly foliated group, and (2) a younger, non-foliated 

 group, characterized by the predominance of soda-bearing types. 



Folded and faulted rocks of Cretaceous age are found in the valleys 

 of the Benue and the Gongola. They consist of a lower series of 

 sandstones and grits, in places salt-bearing, and an upper series 

 of limestones and shales wdth numerous fossils of Turonian age. 

 These Cretaceous rocks are overlain unconformably by a horizontal 

 series of sandstones, grits, conglomerates, and ironstones, which in 

 Sokoto province contains intercalations of Middle Eocene limestones. 

 Considerable volcanic activity occurred during Tertiary times, and 

 gave rise to extensive fields of basaltic lava in Bauchi and Bornu, 



