Association of American Geologists and Naturalists. 159 



River limestone, which expands greatly in thickness, becomes more 

 highly magnesian, and acquires some fossils not seen to the northeast. 

 But beyond the neighborhood of New Market in Virginia, the changes 

 ai'C much more important ; for with the magnesian limestone is asso- 

 ciated a vast body of chert, and the Utica slate as a stratum disappears ; 

 the place of that rock and the Trenton limestone and Hudson River 

 slate, being occupied somewhat as in Ohio, with a blended calcareo- 

 argillaceous mass, in which neither formation is distinctly recognized, 

 and where the fossils of each are to a considerable extent intermingled ; 

 the Lingula rectilateris^ for example, deemed characteristic of the 

 Utica slate in New York, being found throughout all the middle and 

 southwestern region of Virginia associated with the Cypricardlas, so 

 distinctive of the Hudson River group, and always very high in the 

 series. Entering East Tennessee, but especially in the region of Knox- 

 ville, the middle part of the series represented by the Trenton lime- 

 stone and Utica slate of New York and Pennsylvania, and by the sim- 

 ple attenuation of layers of limestone and slate with Trenton, Utica, 

 and some Hudson slate fossils at Cincinnati and in the interior of Vir- 

 ginia, becomes a complex group of several distinct formations no where 

 developed farther north. 



Thus the entire Matinal series in East Tennessee embraces in the 

 ascending order, 1st, a great magnesian limestone between two thou- 

 sand and three thousand feet thick, with high beds of chert, often oolitic, 

 and layers of white and even red sandstone ; 2d, a knotty argillaceous 

 limestone containing Maclurea, Isotelus, and a great profusion of Cala- 

 mapora, Polymorpha, and other corals, seven hundred feet thick ; 3d, 

 a white encrinal sparry limestone five hundred feet ; 4th, yellowish 

 calcareous slate several hundred feet ; 5th, sandy gray limestone very 

 ferruginous, three hundred feet ? 6th, yellowish or buff slates several 

 hundred feet ; 7th, red and greenish coralline and encrinal marble 

 four hundred ? feet ; 8th, calcareous gray and yellowish slates several 

 hundred feet. 



Upon comparing these Matinal rocks of East Tennessee, with those 

 of the northeastern portions of the basin, the difficulty of establishing 

 an equivalency in the ordinary sense of the term, will be found to be 

 insuperable ; for while the Tennessee strata in the middle part of the 

 column, possess a number of well known Trenton limestone fossils, the 

 minoling of these with Hudson slate species, the total disappearence of 

 others, and the introduction of new forms, preclude every attempt at 

 identification. 



