100 



to add materially to the exact conclusions which have been already- 

 drawn in this class of researches. 



Russia and the Ural Mountains. 



Having occupied your attention during the past session with me- 

 moirs on the Geological Structure of so large a portion of the earth 

 as the Russian empire, I must make a few allusions to a subject which 

 has to a great extent engrossed my thoughts and those of my coad- 

 jutors, M. E, de Verneuil and Count A.Keyserling. Employed as we 

 are in preparing a work explanatory of our views, in which we hope 

 to do justice to all previous inquirers*, and to the Imperial Admi- 

 nistration of Mines which supported us, I Avill not on this occasion 

 venture to occupy moi'e time than will be sufficient to touch upon 

 some of the most striking geological features of that empire, which 

 either sustain or enlarge our views of classification and compai'isou. 



Silurian Rocks. — The Silurian, Devonian and Carboniferous de- 

 posits of Russia, are each characterized by distinct organic remains ; 

 and these rock systems are very clearly separated from each other over 

 enormous spaces. Occupying (including the Baltic islands) a tract 

 as large as the principality of Wales, the Silurian rocks, like those 

 of Norway and Sweden, are unequivocally the oldest fossiliferous 

 strata, since they are seen to repose upon the primary crystalline 

 masses of Finland and Lapland. Little elevated above the Baltic Sea 

 and the rivers of the northern watershed of Russia, these Silurian 

 rocks constitute low plateaus only of limestone, clay and sandstone, 

 often incoherent, and on the whole of very small thickness; thus 

 exhibiting the most obvious contrast to their mountainous and fre- 

 quently sub-crystalline equivalents in Western Europe and the Bri- 

 tish Isles. In their small vertical dimensions they present to us, in- 

 deed, a very instructive lesson, for in passing- from Norway, Sweden 

 and Gothland into Russia, the distinguishing strata thin out, and 

 losing their divisionary lithological characters, part also with many 

 of their characteristic shells. " When followed from one region to 

 another, deposits of all ages exhibit like contractions and expan- 

 sions, dependent on the forms of the ancient bays, the nature of 

 the springs and currents, and the depth of the seas in which they 

 were accumulated f." 



Devonian Rocks. — If the horizontal range of the Silurian rocks of 

 Russia be considered large as respects our terms of comparison, what 

 will my associates say to the expanse over which the Devonian or next 

 ascending group is spread, when I tell them that it is much larger 

 than the whole of the British Isles ? Reposing upon the low Silurian 

 plateaus, this widely ranging deposit rises to heights of from 500 to 



* During its preparation, our general map of the Russian empire has 

 been much improved in its north-eastern extremity, the country beyond 

 Archangel wliich we did not visit, in consequence of the observations of 

 the distinguished botanist M. Ruprecht. 



■\- Geological Researches in Russia (in the press) by Rodericklmpey Mur- 

 chison, E. de Verneuil, and Count A, A'on Keyserling, assisted by Lieut. 

 Koksharof, p. 40. 



