PUBLICATIONS. 353 
Geological Survey of Ohio ; Geology, Vol. VII., by PRorEssor 
EDWARD ORTON, State Geologist, 1893. 
This volume although entitled ‘‘ Geology” is of a more or less 
composite character. It is divided into two parts, the first treating of 
Economic Geology, and the second treating of the Archeology, Bot- 
any and Paleontology of the State of Ohio. These various subjects are 
treated by various authors. Part I. of the volume is divided into four 
chapters : Chapter I. on the Geological Scale and Geological Structure 
of Ohio; Chapter II. onthe Clays of Ohio, their Origin, Composition 
and Varieties ; Chapter III. on the Clay Working Industries of Ohio ; 
and Chapter IV. on the Coal Fields of Ohio. 
Chapter I., by Professor Orton, gives a general summary of the 
various geological formations comprised in the state, with special 
reference to those carrying products of economic value. The Geolog- 
ical structure of the state is also briefly but clearly described, includ- 
ing the Cincinnati axis, the Appalachian folds, and various other 
structural features of the state. 
Chapter II., by Professor Orton, discusses the origin, composition, 
and nature of clays in general, and describes the different kinds found 
in Ohio. The lowest formation in the state known to have been 
worked for clay is the Medina shale in the Upper Silurian, and from 
this up to the Coal Measures numerous other formations contain clays 
of commercial value. The most important deposits are in the Car- 
boniferous rocks, and especially in the coal mining districts where they 
are often directly associated with coal. By far the most extensively 
used deposit in the state is what is known as the Kittanning clay in 
the Carboniferous series. 
Chapter III., by Edward Orton, Jr., is a very exhaustive and 
an exceedingly valuable article on the clay industries of Ohio. He 
shows that the manufacture of clay wares in Ohio has increased 
immensely in the last ten years, so that it is now second only to coal 
mining among the industries developing the natural resources of the 
state. The nature and origin of clays and their chemical and physical 
properties as related to their commercial uses, and the methods of 
testing them, are treated in detail. The present prosperous condition 
of the clay industry of the state is shown to be dependent largely 
upon the manufacture of pottery, paving materials, pipes, refractory 
materials and building materials. Each one of these classes of 
