.Review of Recent Geological Literature. 353 
REVIEW OF RECENT GEOLOGICAL 
LITERATURE. 
Coal Deposits of [<>in,r. By Chakles Rollin Ketes. Iowa Geological 
Survey, vol. n. 536 pp., 221 figures, 18 plates. Des Moines, 1894. This 
volume is uniform in size and style with the first number of the series 
already issued. It is printed on the same heavy paper, and the execu- 
tion is exceptionally good. As is stated in the preface, this report does 
not attempt to cover all the various matters connected with the coal 
which a state survey may properly be expected to investigate. The 
detailed stratigraphy of the various coal seams must of necessity be the 
result of investigations extending over a considerable period of time: 
the determination of the best methods of mining and forms of mining 
machinery also forms a subject in itself; the studies on the properties 
of the Iowa coals and the determination of the most economic use of 
each require long and careful research : each of these subjects has been 
taken up, and in time the results may be expected. The present vol- 
ume comprises 200 pages or more devoted to a consideration of the urol- 
ogy of the Mississippi basin with reference to its bearing oil the Iowa 
Coal Measures. Succeeding this is an equal number of pages devoted to 
the details as exhibited in the various counties. The volume closes 
with a brief consideration of the coal industry. In the first part of the 
book a number of interesting faults are described : and the stratigraphy, 
classification, lithology and geological history of the Carboniferous, both 
Lower and Upper, are treated with a fullness of detail inner before 
attempted in this field. The author has in this summarized the results 
of his work, not only in Iowa, but in neighboring states, and so throws 
considerable light upon the Carboniferous history of the whole Missis- 
sippi valley. The classification of the formations is unchanged, and 
the nomenclature is as used in the previous volume of the Survey. 
In connection with the study of the stratigraphy of the Coal Meas- 
ures are the elucidation of the nature of coal horizons and a harmonizing 
of the various theories which have been from time to lime proposed. 
These are of considerable interest loboth the geologist and the miner. As 
is well known, the earlier workers in the American coal fields held si rough 
to the idea of the parallelism of strata, and in accordance wit h t ha! 
idea the individual coal seams were in many cases believed to be prac- 
tically coextensive with the Coal Measures area. In recent years, how- 
ever, detailed st i id \ has led rather to the other extreme, and the remark- 
able discontinuity of i he coal seams has been emphasized. It has been 
shown time and again that, in this held at least, individual seams 
rarely have more than a ver\ limited extent, Yei i he fa el remained thai 
coal was more usually found at certain levels than at others. for ex- 
ample, nearly one-fourth of the total outpul of the state conies from 
within fifty feel of the base of the Coal Measures. These and numer- 
ous ot her apparently opposing facts are happily reconciled b} 1 1 xpla- 
nation of the real character of coal horizons: thai Stretching "ill 
