Review of Recent Geological Liternture. 273 
be only a tenth oi- fifteenth part of the time since the more extensive; 
Kansan glaeiation, which itself had an unestimated duration and was 
preceded by the still less known Aftonian and Albertan stages, w. u. 
Geologi/ of Johnnon County. By Samuel Calvin. From Iowa Ge- 
ological Survey, vol. vii (Annual Report for 1897), pp. 33-116, with two 
maps, two plates, and ten figures in the text. Silurian, Devonian, and 
Carboniferous formations, with overlying Kansan and lowan drift and 
loess, form this county, lying in the southeast part of Iowa. Its largest 
town, Iowa City, was the first capital of Iowa, and is the seat of the state 
university. 
At the State Quarry, worked for the new capitol at Des Moines, it is 
found probable that the heavy-bedded limestone of the quarry is of Up- 
per Devonian age, being of small area and deposited in a deeply eroded 
hollow of the adjoining Cedar Valley limestone, of Middle Devonian age. 
Both formations are nearly horizontal, but between their times of depo- 
sition the sea bed here appears to have been temporarily elevated to be 
dry land channelled by streams. 
The Kansan till was much eroded, and Vjecame superficially oxidized, 
while its carbonate of lime near the surface was removed by the growth 
of plants and the leaching effect of percolating water, and its granite 
boulders suffered decay, before the much later lowan stage of re-advance 
of the ice-sheet. The lowan till has undergone none of these changes, 
showing that its age is far more recent. Of this later till Prof. Calvin 
writes: ''Oxidation is not more marked at the surface than in the deep- 
er parts of the deposit. Calcareous matter is about as abundant at the 
gra.ss roots as it is ten feet lower down. The bowlders are sound and 
hard, showing no signs of decay." The lobate border of the lowan drift 
is marked by moraine hills which rise 40 to 80 feet above the general 
level of the contiguous plain. Southward the loess, derived from the 
melting lowan ice-sheet, overspreads the Kansan drift. It also occurs 
in ridges, called by McGee paha, within the area of the lowan till, these 
being of similar origin as the sand and gravel eskers of other regions. 
The drift deposits of Johnson county vary greatly in depth, and their 
maximum exceeds 250 feet. The very irregular surface which had been 
produced by a period of erosion immediately preceding the earliest gla- 
eiation was changed by the deposition of the drift, so that it is now 
mostly a moderately undulating or nearly level expanse, only rarely 
broken by projecting preglacial hilltops. 
Following the geological report, Prof. T. H. Macbride gives a list of 
the forest trees of the county: and Dr. C. R. Eastman contributes an 
important preliminary report of eight pages, with a plate, on the Devon- 
ian lung-fishes whose teeth occur in great abundance in a bed of the 
State Quarry. w. u. 
A Treatise on Rocks, Rock-weather ing and Soils. By George. P. 
Merrill. (8vo, xx and 411pp., 25 pis.- and 42 fig.?.; New York, The 
Macmillan Co., 1897. Price §4.00.) The first two parts of the book com- 
prising 172 pages, are devoted to a discussion of the rock-forming min- 
erals and of rocks, including their classification and general character-, 
istics. While the author states that this work is to be considered in no 
