316 Reviews-—Holl’s Formation of the Malvern Hills. 
needed, are to take place without elevation and subsidence of the 
ground beforehand ? 
A theory has been lately put forward by Prof. Bischoff, too late 
for notice in this Memoir, that elevation and depression ‘ have re- 
sulted from an increase or decrease of volume in deeply seated rocks, 
in consequence of the more or less complete displacement of the — 
silica of their silicates by carbonic acid.’ * 
We cannot forbear quoting a passage from the close of this Ap- 
pendix :—‘ A study of the existing state of any portion of the earth’s 
surface will show that denudation is, in fact, more a hill-maker than 
a hill-destroyer. . . . In what I say here, I, of course, allude to sub- 
aérial, pluvial denudation, by rain and rivers. Oceanic denudation 
may perform a greater amount of work in abrading and transporting 
matter; . .. but, as a rule, and as compared with pluvial denuda- 
tion, it is purely a levelling agent; it carries away wholesale where 
the other agency would work out mountain-systems on its own prin- 
ciples.’ The relation of the two kinds of denudation has been ably 
worked out by Prof. Ramsay for the district of the Weald. 
It is not a little strange that the advocates of theories of atmo- 
spheric denudation should be chiefly found, of late days, in the ranks 
of our Geological Surveys,—Ramsay, Jukes, and Logan being fol- 
lowed by Medlicott, Geikie, and others; and we think it not a small 
thing in favour of these views, that they are upheld by those who, of 
all men, should know something of that ‘form of the ground’ by the 
careful and detailed examination of which they get their living. To 
Hutton, Playfair, and Scrope belongs the honour of being the earlier 
advocates. 
With the Memoir is a map, on a scale of eight miles to an inch; 
and there are also three lithographic plates, as indistinct as is usual 
with that style of illustration, and many woodcut sections. The 
‘vet up’ contrasts very favourably with the thin paper and crowded 
type of our own Geological Survey Memoirs, which, we feel assured, 
would be thought more of were they printed as they should be, and 
not sacrificed to a miserable and mistaken notion of Governmental 
economy. 
To conclude, the work, which is a credit both to its author and 
to the Geological Survey of India, should be read by every philo- 
sophical geologist. ; 
On THE ForMATION AND History or THE MALveRN Hints. By 
Dr. H. B. Hot, F.G.S. [Quart. Journ. Geol. Soc., No. 81, 
February, 1865. | 
pee principal object of this valuable paper is to show that the 
rocks which constitute the axis of the Malvern Range, and which 
have hitherto been treated of as syenite, &c., are in reality of Meta- 
morphic origin, and consist of a variety of gneissic and schistose rocks, 
* Quarterly Journal of Science, vol. i. p. 475 (June 1864). 
t The Physical Geology and Geography of Great Britain, 2nd edit., 1864. 
