THE CARBONIFEROUS SYSTEM. 113 
ceological series? viz., every where. It is found in considerable quantity 
in the oldest rocks known, the Laurentian; hence all the mechanical 
sedimentary strata derived from the erosion of the Hozoic 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- 
eists 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 
ereat 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 
8 
