llevieu: of liecent Geolociical Liferotvre. 259 
the chief rock of the great Lyakhoff Ishind. and which, as IJaron Toll's 
observations now prove, are remains of the gn-at ice-shecl wliich for- 
merly covered both the jslands and the mainland, and whdse moraines 
have now been discovered on the mainland. Moreover, these ice ma.sses 
have the typical <irannlated structure of the frlacier ice, which proves 
that they have originated from the snow-cover, and could not have 
originated from any sort of running water. As to the P()St-(Jiacial lay- 
ers which overlie the above, they contain, besides shells of (Ujclaa and 
Valrata and well-preserved insects, full trees (yi Alnuxifruiicimn, willows, 
and birch, fifteen feet high, and bearing perfectly well-preserved leaves 
and cones. The nortliern limit of tree vegetation thus spread during 
the Mammoth period full three degreesof latitude higher than it spreads 
now, i. e., up to the 74th degree, and the mammoths and rhinoceroses of 
the time lived upon the patches of meadow clothed with the above 
bushes. It is worthy of note, that the masses of underground ice are 
not found in the lower parts of the Arctic coast which are known to 
have been covered by the Post-Pliocene sea. and that they only occvir 
where the land rises a few hundred feet above the present level of the 
sea — that is, above the level of the Post-Pliocene ocean. w. u. 
REVIEW OF RECENT GEOLOGICAL 
LITERATURE. 
Manual of Geology, treating of the princijileif of the fieienre irith fiperial ref- 
erence to Amerienn geological history. By James D. I).\n.\. 10S7 pages; 
1575 figures in the te.xt; and two double-page maps. Fourth Edition. 
(American Book Co., 1895.) The first edition of this Manual was 
brought out in 1802, the second in 1874, and the third in 1880. After 
having been before the public a third of a century, and after its author 
lias been engaged in geolog.v and zoology during sixty years, the Manual 
in the present edition includes frequent illustrations and examples (as 
on pages 206, 280, etc.) of geological processes and principles from the 
author's observations during all these years, in which he has seen the 
science vastly expanded and the geologic exi)loration of North America 
and all other parts of the world carried forward until now few large dis- 
tricts remain entirely unknown as to the history recoriled in their rock 
formations. 
Professor Dana's studies of coral islands and of volcanoes during his 
voyage in the Wilkes Exploring Expedition, in 18:58 to 1842, and in his 
visit to the Hawaiian islands again, in 1887, have given a special value 
to his discussion of these subjects; and his doctrine of the gradual 
growth of N<»rth America as a tyi)ical continent, first announced in 
1840, has well stood the test of a half century of raiiidly progressing in- 
vestigation and theories. Throughout the volume, as in Lyell's works, 
a prominent and stimulating feature is thf brief rcfiM-enci' to discover- 
