REVIEW OF GEOLOGICAL STRUCTURE. Oil 
in the form of continuous strata from one to four feet in thickness. The 
discovery of these beds of iron ore adds greatly to the value of the min- 
eral lands of Perry and Hocking counties, and has induced the erection of 
many new furnaces there. These are now manufacturing iron at a cost 
of not more than $12 to $15 per ton—a less price than it costs in any 
other part of the country. The excellence and abundance of the coal 
of this region had before been sufficiently proven, and it is now stated 
by Mr. Read that the iron ores associated with it exist in such quantity 
that they are not likely to be first exhausted. 
A re-examination of the Coal Measures of the region lying south of 
the Hocking Valley coal field, in the counties of Jackson, Vinton, Gallia, 
and Meigs, has been undertaken by Prof. Edward Orton, and his report, 
now published, will be found to contain much interesting and valuable 
information in regard to the coal and iron mines of this rich district. 
The reports on the geology of a number of the coal-bearing counties 
north of the National road are contained in the present volume, and the 
reader is referred to them for details illustrating the general description 
of the Coal Measures given in Volume I. 
SURFACE GEOLOGY. 
In Vol. II of this Report, a chapter of eighty pages is devoted to Sur- 
face Geology, and a somewhat detailed description is given of the Drift 
phenomena which had been observed in Ohio, with a sketch of the his- 
tory they seemed to teach. Since the publication of that volume a large 
number of papers on the Drift have been issued in this country and in 
HKurope, and new editions of Croll’s ‘Climate and Time,” and Geikie’s 
*““Great Ice Age” have appeared. In some of these the facts and conclu- 
sions of Chapter XXX have been made the subject of comment in such 
a way as to show that they have not always been understood. A few ad- 
ditional notes on our Surface Geology are therefore required to explain 
more fully the facts reported or views advanced, or to correct some mis- 
takes and misstatements which have been made in regard to them. 
BURIED CHANNELS. 
In the earlier notices of the system of deeply excavated, and now buried 
drainage lines, which are found beneath the superficial deposits of Ohio, 
and many other parts of North America, published by the writer, * they 
were referred to the glacial epoch, but in a subsequent paper} they are 
* Proceedings Bost. Soc. Nat. Hist., Vol. X, 1862. 
t Surface Geology of the Basin of the Great Lakes. Annals Lye. Nat. Hist., N. Y., Vol. 
IX, 1869. 
