170 



THE GEOLOGIST. 



carboniferous series^ containing coal-measure plants, but no 

 workable seams of coal occur under the uppermost group. 

 Beneath the sandstone formation a distinct series of strata 

 commences^ though the inclination of the beds is conformable 

 to that of the carboniferous deposits. It has been termed 

 by Professor Rogers, the Appalachian system, and consists 

 of nine formations, arranged in the following descending 

 order : — 



1. Red and buff-coloured shales and argillaceous sand- 

 stones. 



2. Olivaceous shales. 



3. Fossiliferous sandstones. 



4. Argillaceous blue limestone- 



5. Variegated calcareous shales. 



6*. White and yellowish fucoidal sandstones. 



7. Red argillaceous shales and soft red sandstones, with 

 hard, greenish, and dark grey sandstones. 



8. Dark blue, drab, and yellow slates. 



9. A thick blue limestone. 



The entire thickness of these formations is estimated to 

 be at least 10,000 feet. The lowest limestone (No. 9) has a 

 great range, extending through Pennsylvania and New York 

 to lake Champlain and the banks of St. Lawrence, and it is 

 considered, on account of its organic remains, assignable to 

 the lower Silurian rocks of Mr. Murchison. The whole of 

 the foregoing series, including the carboniferous deposits, are 

 contained within a gigantic trough, which ranges from north- 

 east to south-west, and is traversed, to a greater or less extent, 

 by seven remarkable parallel ridges, ten to twelve miles dis- 

 tant from each other, and presenting the appearance of a 

 series of concentric segments of circles, with the convex sides 

 towards the north-west. These ridges are also parallel to the 

 great range of the Alleghany and Appalachian mountains, 

 increasing in sharpness and importance as they approach 



