116 Horner's Geological Address. 



found in undoubted Jurassic beds, it becomes doubtful whe- 

 ther the mere " resemblance as a group " of the plants in the 

 Virginian beds is conclusive evidence, opposed as it is by the 

 lithological character of the deposit, and the most remark- 

 able circumstance of the entire absence of the oolitic series 

 in any other part of the American continent. In a letter I 

 had from Mr Lyell, who last December passed through Vir- 

 ginia, he informs me that he had seen some specimens of 

 coal plants and ichthyolites from this deposit, which throw 

 some doubt on its being of the oolitic age, especially when 

 he compares the list with those from Connecticut, and that 

 he intends to return to the spot in April next, in the hope of 

 being able to determine their true age more precisely. 



The only member of the oolitic series found in Russia is a 

 representative of our Oxford clay and the beds immediately 

 associated with it, — that which the French geologists call the 

 Terrain Oxfordien, Nor, where these Jurassic beds occur, do 

 they occupy any great extent of surface, but are in detached 

 spots, at remote intervals, in isolated basins, patches or 

 stripes. They are composed of slightly coherent dark-colour- 

 ed pyritous shales, sands and calcareous concretions, sand- 

 atones and marlstones, very seldom solid calcareous beds, and 

 throughout with a surprising uniformity of character. They 

 are besides of little vertical thickness, compared to the same 

 series in other countries of Europe, the most considerable not 

 exceeding 400 feet. They form low masses, which no doubt 

 were at one time more connected, and have been subjected 

 to powerful denuding causes. They extend from the plains 

 of Prussia to the frontiers of Asia on the east, and to the 

 Frozen Ocean on the north. They are moreover seen to un- 

 derlie the cretaceous and tertiary deposits of Southern Rus- 

 sia, and appear in the steppes which lead from Europe into 

 Asia ; but in these southern regions they undergo a change 

 in lithological characters ; becoming siliceous and calcareous 

 grits, and resembling the conglomerates and grits found at 

 the base of the oolitic series in some parts of England ; their 

 fossil contents, however, continue the same. 



