88. Horner' & Qeological Address. 



Russia, are little disturbed from their original horizon tality, 

 making the order of their relative positions clear and unequi- 

 vocal in both countries. In lithological characters there is 

 a considerable resemblance on both sides of the Atlantic — 

 mudstones, sandstones, and limestones prevailing. In Ame- 

 rica, however, there is an intercalated group in the Upper 

 Silurian system, to which nothing analogous has yet been 

 observed in Europe, as far as I am aware. It consists of 

 red, green, and bluish marls, with beds of gypsum and occa- 

 sional salt-springs, the whole being from 800 to 1000 feet 

 thick, and undistinguishable from parts of the Upper New 

 Red Sandstone or Trias of Europe. A similar intercalated 

 group of red and green argillaceous marls, with gypsum and 

 salt-springs, is met with in the middle of the Devonian group 

 in Russia. This occurrence of gypsum and muriate of soda 

 associated together in the older strata, as they are in the 

 Pliocene, as well as in many intermediate periods, is a re- 

 markable circumstance ; and it would be an investigation 

 well deserving the joint labours of the chemist and the geo- 

 logist, to endeavour to account for the origin of these chemi- 

 cal formations. 



With regard to the fossil contents of the Silurian beds of 

 North America, it appears that " while some of the species 

 agree, the majority of them are not identical with those found 

 in strata which are their equivalents in age and position on 

 the other side of the Atlantic. Some fossils which are iden- 

 tical, such as Atrypa affinis, Leptizna depressa and Leptcena 

 euglypha, are precisely those shells which have a great verti- 

 cal and horizontal range in Europe — species which were 

 capable of surviving many successive changes in the earth's 

 surface, and for the same reason enjoyed, at certain periods^ 

 a wide geographical range. It has been usually affirmed 

 that in the rocks older than the carboniferous, the fossil 

 fauna in different parts of the globe was almost everywhere 

 the same ; but Mr Lyell adds, " that, however close the gene- 

 ral analogy of forms may be, there is evidence in the Silu- 

 rian rocks of North America of the same law of variation in 

 space as now prevails in the living creation ;" and in another 

 place he states, that, with regard to the proportion of species 



