437 



1st, That the coast around the Bay of Dublin has been elevated, 

 though unequally, at a comparatively recent geological epoch ; 2ndly, 

 That the valley of Glenismaule, and other valleys containing similar 

 accumulations of drift, were at one time under water, and then filled 

 with calcareous gravel ; and that they were afterwards elevated, and 

 subsequently re-excavated by the action of running water. 



The memoir concluded with some theoretical observations respect- 

 ing the sources from which the calcareous gravel was derived, and 

 the agents by which it was brought into its present position. 



A paper " On the Geology of the Thracian Bosphorus," by Hugh 

 Edwin Strickland,Esq.,F.G.S., and William John Hamilton, Sec.G.S., 

 was then read*. 



The formations which occur in the neighbourhood of the Bosphorus 

 may be classed as follovii's : 1. A series of beds considered to be equi- 

 valents of part of the Silurian system ; 2. Igneous rocks ; 3. Tertiary 

 limestone ; 4. Ancient alluvium. 



1. The equivalents of the Silurian system occupy both sides of the 

 Bosphorus for about three quarters of its length, and extend in Eu- 

 rope and Asia towards the W.N.W. and E.S.E. to an unascertained 

 distance. The prevailing rock is argillaceous schist, but associated 

 with it are compact brown sandstone, and compact dark blue lime- 

 stone, the whole passing insensibly into each other. Andreossy 

 and an American traveller referred the deposits to the transition 

 class, on mineralogical characters ; and the authors of this memoir, 

 to that portion of it lately named Silurian by Mr. Murchison, from 

 the general agreement of the organic remains to those found in the 

 formations beneath the old red sandstone in England. Fossils are, 

 however, of so rare occurrence that Messrs. Strickland and Hamilton 

 noticed them at only two localities, a ravine above Arnaout-keui, about 

 four miles from Pera on the European side 5 and the Giant's Moun- 

 tain on the Asiatic side of the Bosphorus, and about fifteen miles from 

 Constantinople. At the former locality they were found in argilla- 

 ceous schist, and in the latter in limestone. They belonged chiefly to 

 the genera Spirifer, Productus, Terehratula, Atrypa and Orthis ; but 

 the eye of an Asaphus, remains of Crinoidea, and of three genera of 

 Corals were also obtained. 



2. Igneous Rocks. — The transition rocks are united on the north to a 

 mass of igneous rocks, and on the south-west to tertiary deposits. 

 The authors were unable to determine the relative age of these two 

 formations ; but as the igneous rocks are brought into more immediate 

 connexion with the Silurian or transition group than the tertiary, they 

 are described first. They consist of trachytes and trachytic con- 

 glomerates. The former are more or less compact, sometimes passing 

 into phonolite and basalt, and occasionally assume a columnar struc- 



* In a note, Mr. Strickland says, that Mr. Hamilton being still in Asia 

 Minor, he has been deprived of any direct assistance in drawing up this 

 paper; and that he is solely responsible for any theoretical views which it 

 may contain. 



2 i2 



