2904 STUDIES FOR STUDENTS 
de Launay, and Suess; but the book is far more than a perfunctory 
comparison. It is only necessary to examine with care a few chapters 
to see that the author has given to each province conscientious study 
and has brought to his aid the latest researches of individual workers 
whose papers are not included in the generalizations of his predeces- 
sors. It is enough to say that the new volume constitutes a masterly 
work to which the future generation of geologists will find it necessary 
often to refer. 
The earth’s mobile zones—The generalization of de Montessus, 
that the areas of high seismicity upon the earth’s surface correspond 
in position to the geosynclinals as mapped by Haug," makes it neces- 
sary that the valuable contribution of this savant be examined 
carefully. Wholly apart from this relationship, however, the paper 
is of great interest in itself, and should be especially so to Americans. 
The conception of a geosynclinal is due to James Hall,? though 
the name was first applied by Dana,3 who ascribed its folded struc- 
ture to lateral compression, and not to the weight of the sediments, 
as did Hall. According to Hall, an enormous accumulation of sedi- 
ments has followed certain zones of the earth’s surface through gradual 
depression of the sea-floor along these belts; his law being that the 
line of greatest depression coincides with the line oj greatest accumula- 
tion, a proportion being thus established at each point between the 
thickness of sediments and the amount of depression. The mountain 
chains form over the geosynclinals, a classical example being furnished 
by the Appalachian system. ‘These generalizations Suess has supple- 
mented by showing that within the folded regions the sedimentary 
series is generally complete and has a certain pelagic character, 
whereas in the unfolded districts one finds lacunae and intercalations 
of brackish water deposits.4 
While Hall insisted that most of the sediments of the geosynclinals 
had their origin in shallow water, Suess referred to them as having 
a certain pelagic, and Neumayr even an abyssal, character. Haug’s 
t Emile Haug, “Les géosynclinaux et les aires continentales,’’ Bull. Soc. géol. 
France, 3 Ser., Vol. XXVIII (1900), pp. 617-711. 
2 James Hall, Nat. Hist. of New York: Paleontology, Vol. II, p. 70 (Albany, 
1859). 
3 J. D. Dana, Manual of Geology (2d ed., 1875), p. 748. 
4 Ed. Suess, Die Entstehung der Alpen (1875), p. 98. 
