Review of Recent Geological Literature. 395 
Elements of Geology, a Test-Book for Colleges and for the General 
Reader. By Joseph Le Conte; revised and partly rewritten by 
Herman Le Roy Fairchild. Fifth Edition, revised and enlarged, 
with new plates and illustrations. Pages xii, 667; with 1002 figures 
in the text. New York: D. Appleton & Co., 1903. 
Seven years have passed since the last previous revision of this most 
popular text-book of geology in use by colleges and universities of the 
United States ; and twenty-six years since its first edition. Although 
Dana's Manual is indispensable for the field worker and specialist, this 
less detailed, but yet widely comprehensive work is generally found more 
satisfactory for class instruction. Both treat very largely of American 
geology, and arc therefore desirable for American students; while the 
grand English text-book of Sir Archibald Geikie, just now appearing 
in its fourth and enlarged edition, deals more fully with the geology of 
the British Isles, and of all the eastern hemisphere. 
Professor Fairchild, since the' death of Le Conte two years ago, has 
extensively revised this volume, strengthening it in many parts by the 
latest results of geologic researches throughout the world, and especially 
from the geological surveys of the United States and Canada and of the 
various separate states. Some sections have been largely rewritten, and 
several new topics are inserted; in which, as is remarked in the preface, 
"the spirit and style of the revered author have been held as the model." 
.distance is acknowledged to John M. Clarke, on Paleozoic inverte- 
brates; David White, Paleozoic and Triassic plants; T. W. Stanton. 
Postpaleozoic invertebrates ; C. R. Eastman, fishes ; F. E. Lucas, reptiles 
and mammals ; C. E. Dutton, earthquakes ; C. R. Van Hise, metamorph- 
ism ; T. C. Chamberlin, earth genesis, eto. Ma-ny new illustrations ap 
pear, including a large number from photographs, which add greatly to 
the attractiveness and instructiveness of the work. 
The planetesimal hypothesis of the genesis of the solar system, in- 
cluding the earth, as recently advocated by Chamberlin, differing much 
from the nebular theory of Laplace, and from its meteoritic modifications 
by Lockyer and G. H. Darwin, is thought to afford to geology a vastly 
extended duration of the earth and sun, far exceeding former computa 
tions by astronomers. 
Postglacial time, the unit from which geologic estimates of the age 
of the earth have been made, in combination with probable ratios of th^ 
preceding long periods and eras, is left without decision in favor of 
either the geologically short period of about 7.000 years, thought by 
some to measure the erosion of the Niagara gorge, or the long period 
of 70,000 years which is advocated by others. But a preference for th : 
lower estimate is perhaps shown by the acceptance of Prof. N. H. Win- 
chell's computation of about 8,000 years as the time required for the 
erosion of the Mississippi river gorge between Fort Snelling and Min- 
neapolis, cut by the Falls of St. Anthony since the Ice age. From the 
studies of Niagara by Wright and by the present reviewer, coinciding 
approximately with that of Winchell and with the large number of esti- 
mates and computations for the length of the Postglacial period, col 
