164^ PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



remains of innumerable shells of the genus Lingula. They are in 

 such profusion as to form black seams like mica, for which they 

 were at first mistaken. It is highly interesting, that in this lowest 

 fossiliferous bed, one of its commonest organic remains should belong 

 to a living genus, and that its form should come very near to species 

 now existing. Throughout so vast a series of ages has Nature 

 worked upon the same model in the organic world ! " 



The Silurian system of the northern countries of Europe is, as a 

 whole, closely analogous to that of Great Britain ; and it proves 

 that wherever the sediments of the same age in the two regions re- 

 semble each other in lithological texture, such similarity is accom- 

 panied by a close approximation and frequent identity in the asso- 

 ciated organic remains. When the fossils from the Silurian beds of 

 Northern Europe were compared, Mr. Lyell informs us, by M. de 

 Verneuil with those brought by him from America, there was a 

 great distinctness ; but the representation of generic forms, whether 

 in the organic remains of the Upper or Lower Silurian strata, was 

 most clear and satisfactory. The geologists of New York make three 

 distinct groups in the Lower Silurian, and four distinct groups in the 

 Upper Silurian series of that country, and Mr. Lyell is of opinion 

 that these divisions are based on sound principles ; that is, on mixed 

 geographical, lithological and palaeontological considerations; the ana- 

 logy of European geology teaching us that minor subdivisions, how- 

 ever useful and important within certain limits, are never applicable 

 to countries extremely remote from each other or to areas of inde- 

 finite extent. The Silurian rocks are developed in North America 

 on a great scale, and like those of Russia are little disturbed from 

 their original horizontality, making the order of their relative posi- 

 tions clear and unequivocal in both countries. In lithological cha- 

 racters there is a considerable resemblance on both sides of the 

 Atlantic — mudstones, sandstones and limestones prevailing. In 

 America however there is an intercalated group in the Upper Silu- 

 rian 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 occasional salt-springs, the whole 

 being from 800 to 1000 feet thick, and imdistinguishable 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 remarkable circumstance ; and it 

 would be an investigation well-deserving the joint labours of the 

 chemist and the geologist, to endeavour to account for the origin of 

 these chemical formations. 



With regard to the fossil contents of the Silurian beds of North 

 America, it appears that " while some of the species agree, the ma- 

 jority 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 identical, such as Atrypa qffinis, 



