Reviews—Medlicott’s Southern Himalayan Ranges. 315 
and lead are worked; and gold is found in the beds of rivers, ‘even 
in streams which only drain the Sub-Himalayan rocks,’ so that it 
must have ‘a doubly derivative origin,’ because, so far as known, 
it never occurs in veins in any but very old rocks. 
The Memoir ends with an Appendix on Theories of Mountain- 
formation, in which an account is given of the views that have 
been put forward by men of note. First, however, the author 
draws a distinction between physical geography and physical geo- 
logy different from that which is usually held. He would use the 
former with regard to the present ‘ aspects of nature’ and ‘the form 
and position of mountains,’ whilst he looks upon the latter as relating 
to ‘ past activities,’ its object being ‘to investigate the mode of origin 
of mountains.’ This seems to be using the term physical geology 
for a very theoretical matter. 
The chief theories of mountain-formation are:—(1) E. de Beau- 
mont’s, according to which the contraction, by cooling, of the sup- 
posed fluid internal mass of the earth has been the cause of the 
distortion and fracture of the comparatively thin crust. The best- 
known part of this theory is the doctrine that parallel mountain- 
chains are of the same age as regards elevation, and that successive 
convulsions would have their directions in pentagonal symmetry. 
We cannot agree with Mr. Medlicott in being captivated by its 
grandeur, and giving way to a hope that it may turn out right in 
the main; for, as he says, it is ‘ far beyond our actual knowledge of 
geology,’ and therefore has really little to stand on: indeed, we think 
that Mr. Hopkins* has clearly shown its great weakness and incon- 
sistency with known facts.—(2) Mr. Hopkins supposes elevations to 
be caused by the expansion of fluids or gases in vast hollows in the 
earth’s crust, and he seems to think that elevations are far more local 
than is supposed by de Beaumont. The result of elevation would be 
to produce longitudinal and transverse fissures, the former with ‘a 
parallelism to the geometrical axis of the area’ acted on, and the 
latter at right angles to these. ‘This theory is applied by its author 
to the Weald; but we fear that, when the detailed geological exa- 
mination of that district has been finished, many of the lines of 
disturbance laid down by Mr. Hopkins will be found somewhat ima- 
ginary; though, should this be the case, we agree with Mr. Medlicott 
that ‘his paper will retain its value as a discussion of one set of 
conditions. —(3) Prof. H. D. Rogers thinks that the undulations of 
the crust of the earth could have been caused neither by simple 
upward nor lateral pressure; but that they are owing to a wave-like 
motion on the surface of the molten fluid beneath.—(4) The theory 
of Babbage and Herschel rests on the fact that the contour of un- 
derground isothermal lines depends on that of the surface. If the 
surface is changed, therefore, by deposition or denudation, these 
isothermal lines will change also, and an expansion or contraction 
of the rocks will take place, giving rise to disturbance. We would 
ask, however, how the deposition and denudation, to the great extent 
* Presidential Address to Geol. Soc, 1853. 
