216 Observations upon the Geology and Paleontology 



111 this part it changes suddenly and without apparent 

 cause from a tolerably pure limestone to that of a mag- 

 nesian character, and again to a very porous, silicious 

 stone, with numerous small cavities left by the decompo- 

 sition of fossils, which usually have a drusy lining. In 

 these parts the carbonate of lime is almost entirely want- 

 ing, and the fossils, with the exception of a few fish teeth, 

 are found only as casts. In a few localities the mass 

 becomes quite sandy, with barely enough carbonate of 

 lime to serve as a cement to a part of it, leaving inter- 

 stices filled with fine, incoherent sand. The causes which 

 produced these lithological changes are not now apparent, 

 yet, whatever they may have been, they seem to have had 

 little influence on the fauna then living, as their fossil 

 remains are found abundantly distributed through all. 



This cannot be considered as a bed of passage, in the 

 common acceptation of the term, from No. 6 to the mid- 

 dle portion of No. 7, as, beside presenting a well-marked 

 line of division and lithological contrast, it is very fossi- 

 liferous, and contains the same species as the beds below, 

 in as great, if not greater, abundance. Among its fossils 

 are many forms of the most delicate corals and bryozoa, 

 with crinoids of several genera and species. The whole 

 gradually passes into the middle portion, without a defi- 

 nite line of separation, while the fossils of each are indis- 

 criminately mixed, so that in the same mass we find fos- 

 sils of known Devonian species, associated with others 

 of not only Carboniferous types, but Carboniferous spe- 

 cies, — the same species which continue without interrup- 

 tion through the Burlington limestone. 



The middle portion of this bed, some ten or twelve feet 

 in thickness, is a tolerably pure limestone, but in a few 

 localities the irregular interstices between the purer layers 

 of limestone are filled with a friable calcareous sandstone, 

 changing to a fine, incoherent sand, similar to that of the 



