354 THE JOURNAL OF GEOLOGY. 
materials, and their manufacture in Ohio, is then discussed. The 
newest of these industries, and the one which has shown the most 
marked increase, is the manufacture of paving materials-which, in the 
form of vitrified bricks, have been shown to have remarkable endurance 
even under heavy traffic. The industry has increased at a wonderful 
rate during the past five years. 
This article presents the subject in a clear and concise manner. 
It shows a thorough insight into the clay industry and is sure to be of 
much value to those interested in the development of clay deposits, 
not only in Ohio but elsewhere. 
Chapter IV., by Professor Edward Orton, isa thorough discussion 
of the coal resources of the state, and a résumé of the work which has 
been done by the survey in previous years in this field. The author 
first discusses the origin of coal in general, and shows the gradual 
‘development of the peat theory from the time it was originally sug- 
gested by Leo Lesquereux until the present. The Ohio coal is shown 
to have been formed in long narrow belts following the line of an old 
bay of the Carboniferous ocean, which had for its western limit and 
shore line the gradually rising Cincinnati axis. The coal, therefore, 
is to be expected to occur on lines running parallel to this old shore 
and gradually to disappear in the other direction, z.¢., at right angles 
to the shore. 
The coal-bearing rocks underlie 10,000 square miles in eastern 
Ohio, but coal does not occur throughout all of this area. There are 
fifteen or eighteen seams of coal of economic value, ten of which are 
‘of much importance. In the series of rocks carrying the coal, there 
are twelve beds of limestone, some of marine and some of brackish 
water origin, which are often more or less replaced by iron. 
The value of coal and the wasteful methods of mining and using 
it, practiced in Ohio and elsewhere, are severely criticised. It is 
shown that Ohio has probably, according to two different calculations, 
I2,000,000,000 and 20,000,000,000 tons respectively of available coal 
left, and that if the rate of consumption should advance as it has done 
in recent years until it reached a maximum of 100,000,000 tons yearly, 
the coal of the state would last, according to two different calcuJations 
only one hundred and two hundred years, respectively, while if the 
rate of increase ceased at 25,000,000 tons yearly, the coal would last 
five hundred and eight hundred years respectively, 
The nature and distribution of the different coal seams are dis- 
