310 



PALEOZOIC TIME. 



tion ; while in Nova Scotia, at the Joggins, there are, according to Logan 

 and Dawson, 14,570 feet. The coal-tields in some regions are broken 

 more or less into patches, either by uplifts that have brought lower 

 rocks to the surface, or by the occurrence of overlying deposits. Those 

 of the Interior basin are but little subdivided, while that of the great 

 Appalachian Mountain region is in many pieces, as illustrated on the 

 annexed map of a part of Pennsylvania. Between the various patches, 



from Pottsville to the Lackawanna coal-field, the outcropping rocks are 

 mostly Devonian and Subcarboniferous. 



II. Kinds of Rocks. 



1. Stratification. — The Carboniferous period opened with a marked 

 change over the continent. The Subcarboniferous limestones and 

 shales, which had been formed upon the submerged land, became 



