Notices of Memoirs — Geological Survey of Indiana. 311 



of analyses of coals and other minerals, so as to make known their 

 commercial importance. The Counties surveyed in detail in 1870 

 were chiefly Sullivan, Daviess, and Martin ; and the following were 

 surveyed in detail in 1871 and 1872, viz. Perry, Dubois, Pike, 

 Parke, Ohio, Dearborn, and Switzerland counties, besides a pre- 

 liminary examination of some ten or twelve others, from which 

 a good general knowledge of their geology has been obtained, as 

 well as the continuance of the Block or iron-smelting coal from 

 the northern limits of the Indiana coal-basin to the Ohio river, a 

 discovery of great advantage to the State, for this coal, which is 

 unequalled for smelting iron, may probably induce the building of 

 blast furnaces along the entire eastern margin of the coal-basin. 

 In Indiana there are two well-defined zones (eastern and western), 

 containing apparently some equivalent seams, yet the quality of 

 the coal is quite distinct in each. The eastern area is about 

 450 square miles, and includes bituminous coals characterized, as 

 non-caking or free burning ; the Block-coal belongs to this series, 

 and is so called from the facility with which it can be mined in 

 blocks; it has a laminated structure, and is composed of alternate 

 thin layers of vitreous dull black coal and fibrous mineral coal. 

 The western zone comprises the greatest area, being over 6000 

 square miles, and contains three or more very thick beds of coal 

 besides a number of thin ones. Its eastern boundary is formed 

 by the zone of block-coal, but cannot at present be well defined; 

 it appears however from the Eeport that the block-coal beds 

 change in character, and pass into caking coal in going west. 



From a general study of the Western and Indiana Coal-measures, 

 Prof. Cox concludes that the Carboniferous rocks of the Appalachian 

 and Western coal-fields were formed in two great depressions that 

 gave rise to large inland seas, which communicated with the ocean 

 on the south and west, and covered most of the southern states, as 

 far north as the 35th parallel. A high ridge of Silurian rocks, 

 capped in places with the Devonian, lying in a north-easterly direc- 

 tion across the states of Tenessee and Kentucky, and along the 

 western border of Ohio, and the eastern of Indiana, separated these 

 two seas from each other, and spreading over portions of the two 

 latter states, extended into Pennsylvania, on the east, and Illinois 

 and Iowa on the west, forming an unbroken chain along their 

 northern shores. In these seas were formed the sub-carboniferous 

 rocks, and, as the water became shallow from accumulated sedi- 

 ments, a barrier was formed, which shut out the ocean, and cut off 

 the source of salt-water supply. By the further drainage of a 

 large surface area, the water of these seas became less and less 

 brackish, and the conditions necessary for the accumulation of the 

 coal vegetation were, in this way, brought about so gradually that 

 many marine forms continued to exist, and, by degrees, accommo- 

 dated themselves to the new condition of things (p. 164), It is 

 further inferred that these seas were of unequal depth, for the 

 thickness of the strata in the two coal-fields is very difi'erent, the 

 Appalachian being estimated at 2500 or 3000 feet, whereas the 



