80 Horner's Geological Address. 



to very careful measurements recently made by order of the 

 Russian Government, is now proved to be 83*6 feet below 

 the Black Sea, would require a most extensive series of local 

 observations and levellings around the region occupied by 

 the Steppe limestone, attended with very great difficulties. 

 It is the opinion of some travellers who have carefully ex- 

 amined parts of this region, that, during the historic period, 

 and within modern times, the surface of the Caspian has been 

 diminishing, from the disproportion between the evaporation 

 from so large a surface in that climate, and the sources of 

 supply of water. Whatever portion of the land occupied by 

 the Steppe limestone is now on a level with, and below the 

 level of the Black Sea, may have been laid bare by this gra- 

 dual lowering of the water of the Caspian ; but whatever 

 portion is above that level, and the greatest proportion of it 

 is so. must, it is evident, have been upraised ; and there is 

 abundant proof of volcanic forces being in activity in that 

 region to the present time. To endeavour to trace the direc- 

 tion of the vast body of water that must have been displaced 

 by the upheaved land, as there could be no direct outlet to 

 the ocean, would be an inquiry of great interest ; for it can 

 hardly be doubted that there must be evidence of a deluge or 

 deluges having swept over a large portion of that part of 

 Asia, and more especially if the elevatory forces acted sud- 

 denly. 



As the leading features of the physical structure and the 

 great geological divisions of the continent of North America 

 are well known, I do not think it necessary to give any ge- 

 neral outline of the country described by Mr Lyell in his 

 lately-published " Travels ;" but I shall have frequent occa- 

 sion to refer to the information contained in that work on 

 several points of great importance, in speaking of some of 

 the additions in the past year to our knowledge of the great 

 groups of rocks, and to our better acquaintance with ques- 

 tions of mineral structure, changes in the form of the land, 

 and distribution of organic remains. 



I shall now offer some remarks on the several great groups 



