322 PALAEOZOIC TIME — CARBONIFEROUS AGE. 



West of the Appalachian region, the rock is in part a pebbly 

 sandstone, but often only a fine-grained, arenaceous rock ; and from 

 some portions of the Mississippi basin it is absent. 



Thin beds of coal occur in these conglomerates, and in certain 

 localities they are of workable extent. 



(a.) Interior Continental basin. — In Ohio, Indiana, and Illinois, there are 40 to 

 100 feet of pebbly sandstone; in eastern Kentucky, a sandstone, which is 50 

 feet thick on the Ohio and 250 on the borders of Tennessee; in western Ken- 

 tucky, a conglomerate, called the Caseyville conglomerate. It is probable that 

 these conglomerates and sandstones, referred to the beginning of the Coal mea- 

 sures, belong to this initial epoch of the period. In Arkansas, the novaculite 

 used extensively for hones, and also great numbers of quartz crystals, occur 

 in beds referred to this epoch. 



(b.) Appalachian region. — The grit in Pennsylvania is mostly a whitish sili- 

 ceous conglomerate, with some sandstone layers and a few thin beds of carbona- 

 ceous shale : it overlies the Subcarboniferous shale or sandstone. At Tamaqua, 

 the thickness is 1400 feet; at Pottsville, 1000 feet; in the Wilkesbarre region, 

 200 to 300 feet; at Towanda, Blossburg, etc., where it caps the mountains, it is 

 50 to 100 feet thick. (H. D. Rogers.) 



In Virginia, the thickness is in places nearly 1000 feet: the rock is mainly a 

 sandstone, but contains heavy beds of conglomerate. The conglomerate of the 

 Subcarboniferous, in a similar manner, becomes an arenaceous rock in Virginia. 

 In Alabama, the rock is a quartzose grit of great thickness : it is used for mill- 

 stones. 



(c.) Eastern border region. — In the Nova Scotia and New Brunswick Coal region, 

 a millstone grit has been observed in the Carboniferous district of northern 

 Inverness and Victoria ; but only sandstones overlying gypsiferous rocks in 

 Pictou co., and shales and sandstones at the Joggins. 



2. EPOCH OF THE COAL MEASURES (14 b). 



I. Distribution of the Coal Areas. 



The Carboniferous areas of North America have been pointed out 

 on p. 305. The regions corresponding to the Coal period (black 

 areas on the map, p. 133) are — 



1. The great Appalachian coal field, covering parts of Pennsylvania, 

 Ohio, Virginia, eastern Kentucky, eastern Tennessee, and Alabama. 

 The workable area is estimated at 60,000 square miles. The whole 

 thickness of the formation is 2500 or 3000 feet : aggregate thick- 

 ness of the included coal beds, over 120 feet in the Pottsville and 

 Tamaqua valley, about 62 feet near Wilkesbarre, 25J feet at Pitts- 

 burg. The area is partly broken up into patches in Pennsylvania, 

 as shown in the following map. In the centre of the State, between 

 Pottsville and Wyoming, are the famous anthracite beds, divided 



