64 REPORT—1862. 
action may be very complex, so that it is often difficult or impossible to separate the 
results of one from those of the other at any particular place. Still I believe we 
may generally regard the external form of a mountain-chain as due to marine, and 
the valleys within it as the result of atmospheric erosion. 
Most of you will be aware that the views I have thus endeavoured to place be- 
fore you are not altogether original ; other persons have before now proposed the same 
method of explanation of the form ofground. M. Charpentier long ago referred the 
origin of the valleys of the Pyrenees to the action of the rivers which traverse 
them. Mr. Dana had pointed to the same action as the cause of the wonderful 
system of ravines that furrows the sides of the Blue Mountain range in New South 
Wales, and of the deep ravines separated by knife-edged ridges which radiate from 
the centres of the high islands of the Pacific. I confess, however, that I had, up 
to the present year, hesitated to accept this explanation without reserve ; and there- 
fore, since I am now convinced of its truth, I am anxious to take the earliest oppor- 
tunity of recording that conviction*. 
Mr. Prestwich, in his recent papers read before the Royal Society, has adopted 
the hypothesis of the subaérial deepening of the valleys of the Somme and the 
Seine, and other river-valleys both in France and England, to account for the for- 
mation of the freshwater gravels which he finds on the flanks of those valleys, so- 
high above the present levels of the rivers or of any possible floods. 
Professor Ramsay has in like manner attributed the formation of the hollows in 
which the lakes of Switzerland lie, to the ploughing action exercised on the sub- 
jacent rocks by the action of the glaciers, when far more extensive than now. The 
formation of lakes lying in “ rock-basins,” and not formed by the mere stoppage or 
damming up of a river, had always been a complete puzzle to me until I read ‘a 
fessor Ramsay’s paper in the last Number of the Geological Journal (May 1862), I 
believe his explanation of their origin to be the true one. 
That he and Mr. Prestwich and myself should all, within the space of the same 
twelvemonth, have been compelled to appeal to external atmospheric action as the 
only method of explaining the origin of the different surface-phenomena we were 
studying, is of itself, I think, good evidence that we are all three pursuing the right 
track in our search after truth. 
At the instant of penning this sentence, I see by a newspaper paragraph that 
Dr. Tyndall follows us in his speculations as to the origin of the valleys of the Alpst. 
* Had I not become previously convinced of the extent and power of atmospheric and 
river action in consequence of my own observations, all scepticism must have yielded to 
the proof of it detailed in the admirable Report by Dr. Newberry on the Geology of the 
Colorado River of the West, published by the United States Government at Washington 
in 1861. It was only in February 1863 that I saw this work through the kindness of 
Dr. Newberry, who himself transmitted to me a copy of it. The beautiful maps and 
plates and the numerous woodcuts illustrate the text in a way that puts to shame the 
miserable niggardliness of our own Government in such matters; for here they are either 
committed to the red-tape ignorance of mere clerks whose duty it is simply to curtail 
expenditure, or to the equally uninstructed indifference of higher officials in dread of the 
well-meant but blundering questioning of some man of figures in the House of Commons, 
or still oftener left to the enterprise of some publisher, who has of course his profit to 
make out of the work. An advertisement at the beginning of the American Report shows 
that the Senate of the United States ordered ten thousand extra copies of it to be printed, 
five hundred of which were given to the officer commanding the expedition. 
Dr. Newberry shows in his Report that the wonderful cazons which traverse much of the 
country of California, and some of which are from 5000 to 6000 feet deep, and only wide 
enough for the waters of the rivers to flow through them, have been cut down by those 
rivers through horizontal and quite undisturbed beds belonging to the Carboniferous, 
Devonian, and Silurian periods into the Granite below, and moreover that wide valleys in 
other parts have also been excavated by the gradual action of atmospheric erosion, leaving 
numerous perpendicular torrs, crags, or pinnacles of rock here and there, all showing the 
same horizontal beds. 
+ A subsequent reading of Dr. Tyndall’s paper, and of a notice of it afterwards by Pro- 
fessor Ramsay, showed me that Dr. Tyndall was inclined, at the time of writing it, to 
attribute the Alpine valleys too exclusively to the action of glaciers. The valleys must have 
been commenced and many of them almost completed before the glaciers, although the 
