Geology and Mineralogy. 153 
other. Moreover, the blocks themselves, in all rapidly deteriorat- 
ing rocks, tend to break up on exposure (especially to My oy) into 
with 
d 
out, and the “clay seams” attenuate and pass imperceptibly into 
“dry seams” which finally, in the deeper quarries, nearly or 
was at first supposed that the phenomena could be satisfac- 
torily explained by the contraction theories recently advocated 
by Kinahan (this Journal, last vol., p. 68), Crosby (Geol. Mag., 
viii, p. 416), and others; but from the judicial presentation of the 
whole subject by Gilbert (this Shy ii vol., p. 50) it ap- 
bovis that these theories sia alone inadequa It ma therefore 
ia 
ace iatifal contraction of the same beds when a lighted by 
denudation, and subjected to cooling and Scniciion may 
mae such Hines: re jointage pla 
2. The Climatie Changes of "tothe Geological Times; by J. 
D. Warmny. Part III, 265-394 pp. 4to. C ambridge, 1882. 
Vol. vii, No. 2, of ihe Memoirs of the Museum of Comparative 
Zoology at aad! ada —In the preceding Part of Professor 
Whitney’s work “Climatic Changes of later Geological 
Times,” Wotiead in a recent volume of this Journal,* the author 
) 
in the earth’s climate, and that | it went forward through the suc- 
cessive geological periods uninterruptedly, to the end of the Ter- 
tiary period. In Part IiI, he reaches the further conclusion that 
this gradual change was continued through the Glacial era to 
h wa 
e author makes a comprehensive sti of the present dis- 
tribution and limits of glacier regions, and of the facts illustrat- 
the remar 
‘tie facts reviewed are stated to sustain the propositions—now 
Vol. xxiii, p. 489; and Part I, in vol. xxi, p. 149 
Am, Jour. ser ~Tmin SERIES, Vor. XXV, No. 146.—Feprvary, 1883. 
