186 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



occupying the region around the Caspian, called by Sir R. Murchi- 

 son the Aralo-Caspian or Steppe limestone, in which the univalves 

 are of freshwater origin, associated with forms of Cardiacese and 

 Mytili which are common to partially saline or brackish water. It 

 abounds in many places with freshwater shells, and indeed presents 

 the true and persistent characters of a deposit in an inland sea, and 

 contains no vestiges of corals or other marine bodies. It was ob- 

 served to be in some places between 200 and 300 feet thick, and at 

 elevations of 700 feet above the present level of the Caspian. It pos- 

 sesses an uniformity of character which separates it from any tertiary 

 deposit of Western Europe. 



You are aware that Mr. Lyell read before this Society four papers 

 on the tertiary deposits of the United States, which have been pub- 

 lished in our ' Pnoceedings ' ; it is unnecessary therefore for me to 

 give even a brief summary of them, and I shall content myself with 

 stating some of the general results. On the Atlantic side of the Al- 

 leghanies, an area about 400 miles long from north to south, and 

 varying in breadth from ten to seventy miles (with some detached 

 patches further south), is occupied at intervals by tertiary deposits, 

 which in the intermediate spaces are probably concealed by the 

 more modern deposits and alluvium which form the surface. There 

 are extensive tracts of Eocene formations, particularly in the south. 

 Out of 125 species of shells which Mr. Lyell obtained from these 

 deposits, he was not able to identify more than seven with species 

 of the same epoch in Europe. But there are a considerable number 

 of representative species, and an equal number of forms peculiar 

 to the older tertiary strata of America. The Ostrea sellceformis 

 may be considered as representing the Ostrea Jlabellula of the Paris 

 and London basins, and appears to be one of the most characteristic 

 and widely disseminated Eocene shells in this North American 

 deposit. 



The Miocene deposits are of far greater extent than the Eocene ; 

 and there is in them a close affinity of many of the most abundant 

 species with mollusca now inhabiting the American coast, the pro- 

 portion being about one-sixth of the whole, or about seventeen per 

 cent., in those examined by Mr. Lyell, who was able to identify 

 twenty-three out of 147 with living shells. The corals also agree 

 generically with those of the Miocene beds of Europe, the cetacea 

 also agree generically, and the fish in many cases specifically. 



Metamorphic Rocks. 



The theory of metamorphism in its more extended application, in 

 recent times, to the explanation of the peculiar structure of certain 

 stratified rocks, has thrown a clear light upon some of the most 

 obscure and difficult parts of Geology. No geologist will now I 

 presume hesitate to admit, that there is evidence amounting to de- 

 monstration that a permanent source of heat exists in the interior 

 of the earth, widely spread beneath the stony envelopment, and that 

 it has existed at all times. Whether it is local or widely spread 

 under the surface — whether it is constantly maintained or is excited 



