622 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



other hand, the very different fauna regarded as typical of the Kome 

 seems to be confined to the middle and lower parts of the formation. 

 There was much oscillation and, consequently, irregularity in distribution 

 and local variation in character of deposits in the valley troughs during 

 the Cambrian. When these shall have been worked out and the beds 

 classified strictly according to diastrophic criteria, considerable modifica- 

 tions of prevailing views respecting the age relations of local stratigraphic 

 facies will have been introduced. Another confidently expected result 

 will be a more definite age assignment of provincial faunal associations. 

 In the case of the Cambrian deposits under consideration, the revised 

 assignment will greatly reduce the number of species now cited as com- 

 mon to both the middle and the upper Cambrian. 



Upper Camhrian deposits in America — The Appalachian sequence. — 

 The formations comprised in the upper Cambrian of the present work 

 have already been mentioned in a general way, and so far as the areas 

 covered are concerned the formations are arranged in the preceding 

 correlation table according to their known or supposed relations to 

 each other and to the units of the time scale. In the Tennessee basin 

 of the Appalachian Valley, to the east of the Eome barrier, the series is 

 defined as beginning with the Eogersville shale, the underlying unfossil- 

 iferous and not generally recognizable Eutledge limestone being for the 

 present regarded as representing somewhat localized late middle Cambrian 

 deposition. The Nolichucky shale forms the top of the series which thus 

 terminates at the unconformable base of the great deposits of magnesian 

 limestone referred to the Ozarkian system. Between the two shales lies 

 the Marysville limestone, with a thickness varying from 200 to 700 feet. 

 The Eogersville shale seems not to exceed 250 or 300 feet, but the N'oli- 

 chucky usually attains a thickness of over 450 feet and sometimes as 

 much as 750 feet: Both the Maryville and the Eogersville become un- 

 recognizable southwestwardly along the strike of the rocks l)eyond Athens. 

 At the same time the whole series becomes thinner, being only about 600 

 feet in Eogers and Spring creeks, about 10 miles west of Athens. These 

 facts suggest that the Maryville at least laps out southwardly, and that 

 only the Nolichucky extends uninterruptedly into Georgia and Alabama. 



South of Hiwassee Eiver and west of the Eome barrier the upper 

 Cambrian is represented by a single formation — ^the Conasauga shale. 

 Although in places apparently exceeding 1,500 feet in thickness, it is not 

 definitely known that the Conasauga includes more than the N'olichucky, 

 or rather that it includes deposits corresponding in age to the Mar3rville 

 and Eogersville. It seems probable, however, that this is so of the rela- 



