Geological Society. 471 



will be read with great interest • they abundantly vindicate the po- 

 sition of photography as a powerful engine of scientific research, 

 one indeed on which we must depend for our future progress in 

 many fields of inquiry. 



Captain Abney has produced in his Treatise, in a small compass, 

 a valuable addition to our scientific literature, and one with which 

 no one who values the artistic and the scientific aspects of pho* 

 tography can well afford to dispense. 



LXV . Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 895.] 



March 6, 1878.— Henry Clifton Sorby, Esq., F.K.S., President, 



in the Chair. 



rPHE following communications were read: — 



-*- 1. " On the Geology of Gibraltar." By Prof. A. C. Ramsay, 



LL.D., F.R.S., and James Geikie, Esq., LL.D., F.R.S. 



In this paper the authors, after giving some account of the 

 physical features of Gibraltar, described in detail the various rock- 

 masses of which the peninsula is composed. The chief rock is a 

 pale grey bedded limestone, overlain by shales containing beds and 

 bands of grit, mudstone, and limestone. Fossils are very rarely met 

 with in the limestone, and have never as yet been found in the 

 shales. The only recognizable fossil they obtained from the lime- 

 stone was a Rhynchonella. which, Hessrs. Etheridge and Davidson 

 think, is most likely Rh. concinna. This would make the beds of 

 Jurassic age. The limestone forms the great eastern escarpment, 

 and dips west under the shales, which form the lower slopes upon 

 which the town is built. The dips vary from 12° or 20° up to 

 vertical. The connexion of these strata with the rocks of the 

 adjoining districts in Spain and the opposite coast of Africa was 

 traced; and it was shown that the Gibraltar Limestone reappears in 

 Ape's Hill in Barbary, while the overlying shales and the sandstones 

 of Queen-of-Spain's Chair form all the ground to the west of Ape's 

 Hill up to Cape Spartel. The Jurassic strata of Gibraltar are over- 

 lain by various superficial accumulations, the oldest of which is a 

 great mass of limestone-agglomerate, which is unfossiliferous, and 

 shows as a rule no trace of stratification. It is made up of angular 

 blocks of limestone of all shapes and sizes, and rests upon an 

 uneven surface of limestone : it also covers wide areas underneath 

 which only shales are present. It is excessively denuded, being 

 worn into ravines and gullies, and presents generally a highly 

 honeycombed surface. Terraces of marine erosion have also been 

 excavated in it. It is not now accreting, and could not have been 

 formed under present conditions of climate and surface. The 

 authors gave at length their reasons for believing it to have been 

 the result of a severe climate. The blocks were wedged out by the 

 action of frost; and the heaps of angular debris thus formed were 



