Notes on American Geology. 247 



Remains of fish and their coproUtes are occasionally found in 

 the middle and upper portions of the transition, but the most dis- 

 tinguishing feature in the palasontology of the system, are the 

 trilobites in nearly all the strata ; the vast proportion of Brachi- 

 opods among the testacea, consisting chiefly of the genera Orthis, 

 Detthyris, and Strophomena or Lept(ena, in the limestones ; gi- 

 gantic quadrangular fucoids in the sandstones, and small linear 

 leaf-like fucoids in the slates. These latter first appeared in the 

 lower slates, where other organic remains are very rare, but occa- 

 sionally trilobites and shells of the genus Strophomena have been 

 found, a fact which induces me to believe that these two orders 

 were, twin-born of the primeval seas, and that they were prece- 

 ded by vegetable life. Mr. Phillips, in his investigation of the 

 English equivalents, has been led to a different conclusion ; but 

 England is a limited theatre for the display of the order of suc- 

 cession, which sinks into insignificance in comparison with the 

 colossal development of the transition in North America. Mr. 

 Phillips observes, " the classes of mollusca are more ancient than 

 those of zoophyta^ if we trust our present knowledge, and both 

 older than marine or land plants."* We have, it is true, as yet 

 no knowledge of zoophyta in the lower slates, and therefore the 

 testacea may be more ancient than they, but marine plants are 

 older than either. 



Among the brachiopodous bivalves, the gemis Strop ho?ne7ia of 

 Rafinesque is the most characteristic of the trilobite system. Pro- 

 ducta has as yet been found only in the upper term, or pyritifer- 

 ous rocks of Eaton, where the species are very few and rare. In 

 the mountain limestone above, Strophomena is hardly known, 

 but it is crowded with Producta of many species. The latter 

 genus, therefore, eminently characterizes the carboniferous sys- 

 tem, with which it ceased to exist. Not a single species of Te- 

 rehratula occurs in the Silurian system of this country, nor have 

 I seen one from the carboniferous ; the shells hitherto classed in 

 that genus being referrible to Orthis. 



Throughout the transition, we very rarely find any evidence 

 of fresh-water streams or lakes ; which is doubtless owing to the 

 very small proportion of dry land in those periods. The first 

 trace of them in New York is in the red sandstone at Medina, 



* Treatise on Geology, p. 289. 



