THE CAEBONIFEROUS SYSTEM. 



113 



geological series? viz., every where. It is found in considerable quantity 

 in the oldest rocks known, the Laurentian; hence all the mechanical 

 sedimentary strata derived Irom the erosion of the Eozoic rocks must 

 contain gold. But it is generally so scattered here as to be practically 

 inaccessible. When these rocks are metamorphosed, however, segregated 

 quartz veins are found and the gold is collected into them. As they are 

 of limited extent and communicate with no possible foreign source of 

 gold, the gold in them must be indigenous. 



THE COAL MEASURES. 



The coal strata of Ohio, though constituting the most interesting and 

 important feature in the geology of the State, have been so fully described 

 in the reports of the Geological Survey already published, and in the 

 various county reports which form parts of this volume, that but little 

 space can, with propriety, be devoted to them here. It should also be 

 said that the distribution, qualities, and uses, of our coals will be discussed 

 at length in the volume on Economic Geology. I shall, therefore, confine 

 myself in this chapter to a brief review of the structure and extent of 

 our coal field, referring the reader to the various reports on the local 

 geology of the State for all detailed statements of the facts upon which 

 the generalizations now made are based. 



The upper division of the Carboniferous system, known among geolo- 

 gists as the Coal Measures ? underlies the surface of the south-eastern 

 third of the State. This, as has been before said, is, with the exception 

 of the Drift, the highest member of the geological series in Ohio. In 

 harmony with the general arrangement of the rocks which fill the 

 great Alleghany basin, the Coal Measures form a series of sheets that, 

 with a general easterly dip, lie on the slope of the anticlinal axis 

 which traverses our State from Cincinnati to the Lake. Over all the 

 eastern half of Ohio the dip of the rocks is toward the east, and all the 

 strata which come to the surface along the middle line of the State are, 

 on our eastern border, buried to the depth of 1000 feet or more. Sharing 

 in this general arrangement, the different elements that compose our 

 coal series form sheets of which the edges come to the surface in lines ot 

 outcrop further and further eastward as we ascend the geological scale. 

 On the northern and western margin of the coal field, only the lower 

 seams of coal and their associated rocks are found, while in going from 

 this line southward or eastward toward the center of the basin the out- 

 crops of one and another of the higher beds of coal are passed over, till 

 on the Ohio, near Wheeling, the surface of the highlands is underlain by 

 nearly 1200 feet of Coal Measure rocks, in which are included ten or 



