REVIEW OF GEOLOGHCAL STETJCTURE. 27 



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. 



SUEFACE 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 

 Europe, 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 f they are 



* Proceedings Bost. Soc. Nat. Hist., Vol. X, 1862. 



t Surface Geology of tlie Basin of the Great Lakes. Annals Lye. Nat. Hist., N. Y., Vol. 

 IX, 1869. 



