REVIEWS 93 
fication, and methods of exploration for iron ore. Chapter iv, on mag- 
netic observations, gives a rather full explanation of the instruments 
used, the interpretation of observations made with them, and their 
capabilities and limitations. 
Part II consists of the detailed township maps and the accompany- 
ing descriptions. Each township is fully described under the following 
heads: surface features, glacial drift, general geology, magnetic obser- 
vations, land classification, and recommendations for exploration. 
Jel, Je 1834 
Coal Resources of District VIII (Danville), Illinois. By F. H. 
Kay and K. D. Wuite. Ill. State Geol. Survey, Coal Mining 
Investigations, Bull. No. 14, 1915. Pp. 68, pls. 7, figs. ro. 
The geology of a part of this district has been described by M. R. 
Campbell in the Danville Folio of the U.S. Geological Survey. The 
present bulletin treats chiefly of the coal resources. The principal coals 
are in the upper Carbondale and lower McLeansboro formations. 
Lenticular masses of shale locally called ‘‘rolls’’ are common within the 
coal beds. Their present shape is the result of depositions in small 
basins and the subsequent settling of the somewhat plastic incompres- 
sible clay into the highly compressible vegetal mass. More than 
58,000,000 tons of coal have been mined in this district since 1880; 
1,494,000,000 tons remain in the ground. HRB. 
Newly Discovered Beds of Extinct Lakes in Southern and Western 
Illinois and Adjacent States. By E. W. Suaw. Ill. Geol. 
Sunvey, Bully 20) rors...) Pp. 141-57. 
During some parts of Pleistocene times aggradation by the Ohio 
and Mississippi rivers exceeded that of certain of their tributaries— 
those which received little glacial drainage. The valley fillings of the 
master-streams therefore dammed these tributaries, and lakes formed 
in their lower courses. The deposits that were laid down in these 
ponded waters are about 100 feet thick at the mouths of the tribu- 
taries and thin out upstream. The Big Muddy River is a typical case. 
Shore features are poorly developed except along the Pond River 
near Madisonville, Ky., 50 miles from the Ohio River. The lakes were 
relatively short-lived, and their levels were subject to considerable 
fluctuations, owing to the great range of high and low water of the 
major streams. 
