330 Geological Society. 



from a true contemporaneous trap. Such altered rocks, however, 

 were quite distinct in microscopic structure from the undoubted 

 lava-flows of the same district, and often distinct also from the 

 Welsh felstones, although some were almost identical microscopically 

 with the highly altered ashes of Wales, and, together with them, 

 resembled the felstone -lavas of the same country. 



This metamorphism among the Cumbrian rocks increases in 

 amount as the great granitic centres are approached ; and it was 

 believed by the author that it took place mainly at the commence- 

 ment of the Old Eed period, when the rocks in question must have 

 been buried many thousands of feet deep beneath the Upper Silurian 

 strata, and when probably the Eskdale granite was formed, perhaps 

 partly by the extreme metamorphism of the volcanic series during 

 upheaval and contortion. The author stated his belief that the 

 Cumbrian volcanoes were mainly subaerial, since some 12,000 feet 

 of ash- and lava-beds had been accumulated without any admixture 

 of ordinary sedimentary material, except quite at the base, con- 

 taining scarcely any conglomeratic beds, and destitute of fossils. 

 He believed also that one of the chief volcanic centres of the district 

 had been the present site of Kenwick, the low craggy hill called 

 Castle Head representing the denuded stump or plug of an old 

 volcano. 



The author believed that one other truth of no slight importance 

 might be gathered from these investigations, viz. that neither the 

 careful inspection of hand specimens, nor the microscopic examina- 

 tion of thin slices, would in all cases enable truthful results to be 

 arrived at, in discriminating between trap and altered ash-rocks ; 

 but these methods and that of chemical analysis must be accom- 

 panied by oftentimes a laborious and detailed survey of the rocks in 

 the open country, the various beds being traced out one by one, and 

 their weathered surfaces particularly noticed. 



November 18, 1874. — John Evans, Esq., E.K.S., President, 

 in the Chair. 



The following communications were read : — 



1. " On fossil Evidences of a Sirenian Mammal (Eotherium cegyp- 

 tiacum, Ow.) from the Nummulitic Eocene of the Mokattam Cliffs, 

 near Cairo." By Prof. Owen, E.E.S., F.G.S., &c. 



The specimens described in this paper were obtained by Dr.. Grant, 

 of Cairo, in a block of the white limestone of the Cerithian rTummu- 

 litic zone, quarried extensively for building-purposes in the Mokattam 

 Cliffs. They consisted of a few fragments of the base of the cranium 

 and a cast of the entire brain with the commencement of the myelon. 

 The author discussed the characters presented by these remains, 

 which he regarded as having belonged to an extinct Sirenian, pro- 

 bably allied to Halitlierium, which he proposed to name Eothermm 

 cegyptiacum. The characters of the brain, as deducible from the 

 cast, were detailed, and shown to be sirenian. By comparison with 

 the brains of other Sirenia, the author was led to trace a progress 

 in the cerebral characters of the animals of this type, from its 



