Geology and Geography. 4^ 



present be attempted towards ascertaining the relative age of the 

 tertiary groups of the two continents, is that derived from a com- 

 parison of the relative proportion of recent to extinct shells. At 

 the same time, Mr Lyell fully concurs with Mr Rogers in his opi- 

 nion, that such a correspondence ought not to be insisted upon, as 

 affording any positive test of exact contemporaneous deposition, 

 since the rate of change in species cannot be assumed to have been 

 always equal, especially in remote regions, during equal periods of 

 time. 



Mr Lyell, in speaking of the adoption by Professor Rogers, of 

 his (Mr Lyell's) nomenclature of the leading divisions of the tertiary 

 formations, remarked, that the principles of his classification had been 

 sometimes mistaken by geologists. Mr Lyell had used the nume- 

 rical proportion of recent to extinct fossil shells, as a useful term of 

 comparison between distinct tertiary groups, but never as the prin- 

 cipal character of a particular epoch. Thus, for example, the im- 

 portant character of the Eocene strata in Europe, was not the cir- 

 cumstance that those strata contain about three per cent, of living 

 species of shells, but that they contain 800 or more species peculiar 

 to the Eocene period, occurring in formations of that era in distant 

 regions, and not found in other tertiary groups. 



Captain Maconochie, Secretary to the Royal Geographical So- 

 ciety, gave an account of the origin and progress of that Associa- 

 tion. He then communicated some details relative to the late ex- 

 pedition to the Niger, and to the expeditions which are about to be 

 sent out to the interior of Africa, and to British Guiana. 



Lieutenant Allan, the fellow-traveller of Lander, exhibited some 

 panoramic views of the scenery of the Niger. 



Mr Murchison presented a tabular view of the order of succession 

 of various formations of great thickness, and distinct from each other 

 in their organic remains and mineralogical characters, which rise 

 from beneath the old red sandstone of England and Wales. He then 

 dwelt on the series of fishes occurring tliroughout the old red sand- 

 stone of England, and pointed out Dr Lloyd of Ludlow as the 

 person who had first called his attention to them. These fishes, it 

 now appears, are common to the central portion of the old red 

 sandstone of Eingland, and the strata occupying the same geologi- 

 cal position in Forfarshire and other counties in Scotland. Mr 

 Murchison fiirther expressed his opinion, that the Arbroath pave- 

 ment is the equivalent of the Tile stones, or lower member of the 

 old red sandstone of England. 



