CARBONIFEROUS AGE. 291 



III. CARBONIFEROUS AGE. 



The Carboniferous age is divided into three periods : — 



I. The SuBCARBONIFEROUS PERIOD (13). 



II. The Carboniferous Period (14). 



III. The Permian Period (15). 



The Carboniferous age, both in America and Europe, commenced 

 with a preparatory marine period, — the Subcarboniferous ; had 

 its consummation in a long era of extensive continents, covered with 

 forests and marsh-vegetation, and subject at long intervals to inunda- 

 tions of fresh or marine waters, — the Carboniferous ; and declined 

 through a succeeding period, — the Permian, in which the marsh- 

 vegetation became less extensive, and the sea again prevailed over 

 portions of the Carboniferous continents. 



American Geographical Distribution. 



The rocks of the Carboniferous age lie at the surface, over large 

 areas of North America, as shown on the accompanying map (Fig. 

 572), in which the black areas and those cross-lined or dotted on a 

 black ground are of this age. 



1. Eastern-border Region. — 1. A small area in Rhode Island, con- 

 tinued northward into Massachusetts. 



2. A large area in Nova Scotia and New Brunswick, stretching 

 •eastward and westward from the head of the Bay of Fundy. 



These two areas are now separated ; but it is probable that they 

 were once united along the region, now submerged, of the Bay of 

 Fundy and Massachusetts Bay. 



II. Alleghany Region. — This great area commences at the north 

 on the southern borders of New York, and stretches southwestward 

 across Pennsylvania, Western Virginia, and Tennessee to Alabama, 

 and westward over part of eastern Ohio, Kentucky, Tennessee, and 

 a small portion of Mississippi. To the north, the Cincinnati geanti- 

 clinal, or the low elevation extending from Lake Erie over Cincinnati 

 to Tennessee, forms the western boundary. 



III. Interior Region. — 1. The Michigan coal area, an isolated area 

 wholly confined within the lower peninsula of Michigan. 



2. The Eastern Interior area, covering nearly two thirds of Illinois, 

 and parts of Indiana and Kentucky. 



3. The Western Interior area, covering a large part of Missouri, 

 and extending north into Iowa, and south, with interruptions, through 

 Arkansas into Texas, and west into Kansas and Nebraska. 



The Illinois and Missouri areas are connected now only through the 



