STRATIGRAPHIC TAXONOMY 039 



and unquestionably of younger types than have been found in the Copper 

 Eidge. The distinctness and superposition of the Chepultepec with re- 

 spect to the three divisions comprised in the typical Knox of Tennessee 

 may thus be set down as reasonably established on both stratigraphic and 

 faunal grounds. All this evidence is repeated in the Cahaba Valley 

 sections. 



The section at the type locality begins in Murphrees Valley at Chepul- 

 tepec Station, which is located on the Conasauga formation, and passes 

 upward through about 300 feet of non-cherty dolomite referred to the 

 Ketona by Butts, t^en through approximately 1,700 feet of Copper Eidge 

 cherty dolomites, then 300 to 400 feet of concealed beds thought to be 

 "upper Knox," followed by about 1,000 feet of cherty magnesian lime- 

 stone — the Chepultepec formation — and unconformably over this by 

 Stones Eiver limestone, which occupies the valley between Chert Eidge 

 and West Eed Mountain. 



Like the Copper Eidge, the Chepultepec limestone seldom outcrops. 

 Both formations are recognized chiefly by the residual chert which accu- 

 mulates on the surface of. the ground with the progress of subaerial decay. 

 On close comparison the cherts of the two formations proved to be readily 

 distinguishable by persistent differences. By far the most of the Copper 

 Eidge chert is white to gray, hard, and of a dense texture, sometimes ap- 

 proaching flint. Occasional layers are oolitic. The Chepultepec chert, 

 on the other hand, is never flinty, but always relatively soft and more or 

 less mealy in texture, and when resistant to the hammer it is because of 

 toughness rather than hardness. Moreover, especially in the upper 300 

 feet, much of the chert is drusy and the masses containing the drusy 

 plates and cavities are soft, wormy, and stained red. 



Fossils are very rare in the lower part of the formation, but are fairly 

 common and in considerable variety in the upper 300 feet. About 20 

 species have been collected from this zone in the vicinity of Chepultepec. 

 The fauna being mostly undescribed, it can not be listed in a satisfactory 

 manner. Perhaps it will suffice to say that it includes ArcheocydtMts ?, 

 Scenella, TJelicotoma nniangnlatum' (Hall). Holopea ? tnrgida Hall, 

 Sinvopea stvecti (? Whitfield), three Tiiospira-like shells, another re- 

 sembling Murchi^onia. putilla Sardeson. Pilocera^ newton-toinchelU 

 Euedemann, Cameroceras, and Orthoreras. 



At least ten of the Chepultepec species occur in the Gasconade forma- 

 tion in Missouri, four in a cherty dolomite near Eoaring Spring, Penn- 

 sylvania : three or more in the chert at the top of the Little Falls dolo- 

 mite at Little Falls, ]^ew York, and three others in the same formation 



