Review of Recent Geological Literature. 57 
high eh'vation which Prof. Geiivie places after his fourth {rlacial epoch 
were instead during preghicial time, bringing on the ice-sheets, low 
shore tracts of the hind bridge to Greenland may never have been 
covered by the ice and so would preserve the Hora for Iceland and 
Greenland when this part of the earth's crust subsided and the Ice age 
ended. 
The duration since the departure of the ice from the ti^mixTate portions 
of Europe and America is thought to have been less than Dr. Croll's 
theory would require. For our continent Prof. Geikie presents Dr. J. 
W. Spencer's discussion of the age of Niagara falls, regarding this time 
as about 32,000 years. Evidence now in hand, however, seems to prove 
that no outflow passed from lakes Superior, Michigan and Huron to the 
Mattawa and Ottawa, on which the greater part of Dr, S[)encer's esti- 
mate is founded. Probably 7.000 years is as close an approximation to 
the duration of Niagara and the Postglacial period as we can attain. 
Twenty years ago the i)resent writer derived his earliest interest in 
our glacial and modified drift from a i)erusal of the first edition of The 
Great fee Age. This third edition will be read by all glacialists with 
much renewal and increasi; of enthusiasm for the many Pleistocene 
(|uestions wiiich still remain debatable. Every page is richly suggestive, 
and the theory of alternating glacial and interglacial epochs has served 
well for the collection and orderly arrangement of a vast mass of infor- 
mation as to the Ice age and its complicated history. w. r. 
T/ie Ore Deposits of the United States. V,y James F. Kemp. iSvo. i>p. i- 
.wii, 1-34:5, with 94 illustrations: revised and enlarged: Scientific I*ub- 
lishing Co., New York and London, 1895.) This work has already been 
reviewed in TiiR Amehkan Geologist (vol. xii, pp. 208-2(59, Oct.. 1893), 
and it is only necessary here to call attention to the revised and enlarged 
edition. '-In the second edition many pages have been rewritten and 
expan(U'(l. The endeavor has been to introduce into the body of the 
work the new materials that have become available in the last year 
This is especially true of iron ores, of the geology of the Sierras and of 
nickel and cobalt. In all some fifty |)!iges of new matter have been 
added, and fifteen cuts." The publication of a second edition of this 
ijook within less than two years after the first edition w;is issued is suf- 
fici(Mit e\ideiice of its usefulness and value. u. s. G. 
The (jeobxjy of Aiujel island. By F. L. Ransom K. With a note on the 
radiolaridii rhert from Angel island and from Buri-huri ridge, San Mateo 
rountg, Cnlifornia. By J. (J. Hinde. (Bull. Dept. of (Jeol. Univ. of Cal- 
ifornia, vol. 1, No. 7, pp. 193-240, pis. 12-14, Oct., 1894.) Angel island is 
three and a half miles north of San Francisco and is compo.sed largely 
of San Francisco sandstone and a jasjjery rock (radiohirian chert). The 
chief geological interest centers in the phenomi-na eoniiecled with (he 
igneous rocks of the island, which are chieliy a large dike of serpentine 
and an intrusive sill. The nu-k of ilir sill varies consideral)ly, but its 
characters seem to ally it mf)re ck)sely with the fourchites described by 
.1. F. Willi.ims from Arkansas than with anv other class of rocks. In 
