22 GEOLOGY. 



part of it which extends from tlie western base of the prinnary 

 rocks to the Chattoogatta range of mountains, and which forms 

 the valley of the Oostanaula river, belongs probably to the 

 older series of the New- York formations, as those portions 

 which have been examined contain Potsdam sandstones, cal- 

 ciferous sandrock and limestones of the Trenton group. Very 

 few fossils have been found in it. At the Chattoogatta range 

 a marked change occurs in the formations, which from that 

 line to the Lookout mountain belong principally to the Helder- 

 berg series of the New-York system, but embrace also the 

 Portage and Chemung groups : and therefore correspond with 

 the middle and upper groups of that system, and with the Wen- 

 lock and Devonian rocks of the English Silurian formation. 

 At the Red Sulphur Springs in Walker county a bed of anlyd- 

 reus limestone occurs, corresponding in character to the up- 

 per bed of the Onondaga Salt group of New- York. Within a 

 few miles of this locality there is a stratum of pentamerus 

 limestone, well characterized by its lithological constitution 

 and abundant remains of pentamerus galeatus. At Gordon's 

 Mineral Springs, at the foot of Taylor's ridge, a stratum of dark 

 shale is found at the bottom of the valley containing Gorginea. 

 Above the shale are successively placed Oriskany sandstone 

 with Atrypa elongata, &c. — a grayish blue, sub-crystalline 

 limestone of the Onondaga limestone group, abounding in cy- 

 athophylla, stylina and encrinital stems, and corniferous lime- 

 stone containing cyathophylla mingled with chert and cherty 

 nodules with crystals of quartz. Above the last lie sandstones 

 of the Portage and Chemung groups. 



Between Taylor's ridge and Pigeon mountain the Onon- 

 daga gray limestone prevails, and is found at the tops of the 

 northern spurs of the latter. A marked change however oc- 

 curs in the crinoidea imbedded in it, and pentremites of the 

 species florealis, globosa and pyriformis take the place of the 

 usual large, smooth encrinital stems. Cyathophylla and favo- 

 sites labyrinthica also occur. Proceeding to the west, on 

 reaching west Chickaumagua creek the Delthyris shaly lime- 

 stone, containing abundant impressions of strophemene appears, 

 and continues to the base of the Lookout mountain. In all 



