XIIL] GEOGNOSY OF THE APPALACHIANS. 255 



Ridge he includes in the primal division (beneath the Calcifer- 

 ous sand-rock) " at least four independent and often very thick 

 deposits, constituting one general group, in which the Potsdam 

 or white sandstone (with Scolithus) -is the second in descending 

 order." This sandstone is overlaid by many hundred feet of 

 arenaceous and ferriferous fucoidal slate, and underlaid by 

 coarse sandy shales and flagstones ; below which, in Virginia 

 and East Tennessee, is a series of heterogeneous conglomerates, 

 which rest on a great mass of crystalline strata. The accuracy 

 of these statements is confirmed by Safford, who, in his report 

 on the geology of Tennessee (1869), places at the base of the 

 column a great series of crystalline schists, apparently repre- 

 sentatives of those of southeastern Pennsylvania. (Ante, page 

 245.) Upon these repose what Safford designates as the Pots- 

 dam group, including, in ascending order, the Ocoee slates and 

 conglomerates, estimated at 10,000 feet, and the Chilhowee 

 shales and sandstones, 2,000 feet or more, with fucoids, worm- 

 burrows, and Scolithus. These are conformably overlaid by 

 the Knoxville division, consisting of fucoidal sandstones, shales, 

 and limestones, the latter two holding fossils of the age of the 

 Calciferous sand-rock. It is noteworthy that these rocks are 

 greatly disturbed by faults, and that in Chilhowee Mountain 

 the lower ' conglomerates are brought on the east against the 

 Carboniferous limestone, by a vertical displacement of at least 

 12,000 feet. The general dip of all these strata, including the 

 basal crystalline schists, is to the southeast. 



The primal palaeozoic rocks of the Blue Eidge were then by 

 Rogers, as now by Safford, looked upon as wholly of Potsdam 

 age, including the Scolithus sandstone as a subordinate member, 

 so that the strata beneath this were still regarded as belong- 

 ing to the New York system. Hence, while Rogers inquires 

 whether the Taconic system " may not along the western bor- 

 der of Vermont and Massachusetts include also some of the 

 sandy and slaty strata here spoken of as lying beneath the 

 Potsdam sandstone," * he would still embrace these lower 

 strata in the Champlain division. 



* American Journal of Science (1), XL VII. 152, 153. 



