422 
NATURE 
ae tae ee 
ps 
[April 3, 1873 
(SS 
nevertheless, quite as much worthy of study as any 
other of the heavenly bodies. If it does not possess 
magnitude of dimensions, it presents an infinite variety 
in all its details. Whole generations, living one after the 
other upon its face, might pass their lives in studying its 
phenomena, without comprehending all their full beauty. 
There is not even any special science, having for its aim 
some portion of the terrestrial surface, or some particular 
series of its products, which does not present to our 
savans an inexhaustible field of inquiry.” 3 
The two first volumes of the work, to which alone we 
must at present confine our attention, consist of four main 
divisions—(t) on the earth as a planet, (2) on the land, 
(3) on the circulation of water, and (4) on subterranean 
forces. The first division treats of the form, structure, and 
motion of the earth, explaining with great lucidity the 
different theories respecting its formation. 
M. Reclus then proceeds to give an outline of the 
geological history of the earth as exhibited by the strati- 
fication of rocks. In places where the strata have re- 
mained undisturbed by the action of the sleepless forces 
ever at work upon the earth’s crust, it is possible to see 
the strata in their regular order of succession, giving, as 
it were, an abstract of the earth’s geological history. 
Probably the most remarkable instance in point is to be 
found in the “ Pyramid Mountain,” the sketch of which 
is taken from the famous “ Pacific Railroad Report.” 
The second division treats of the form and distribution 
of the continents, and points out the wonderful harmony 
and analogy which prevail in the configuration of conti- 
nents and oceans, the arrangement and peculiarities of 
mountain ranges, the origin of valleys, ravines, gorges, 
and other depressions of the earth’s surface. The ques- 
tion of the origin of mountains and valleys is still, 
generally speaking, an open one amongst geologists ; but, 
nevertheless, with regard to valleys and ravines, one can 
in many cases distinctly perceive that their formation is 
due to the ceaseless action of water through countless 
ages, mountain torrents cutting their way even through 
vast mountain chains. Nothing can convey a more 
impressive idea of the tremendous power of water as a 
natural agent, than the wonderful cafions of Mexico, 
Texas, and the Rocky Mountains, where the torrent may 
be seen rushinz along through the incision it has cut out 
for itself in the hard rock at a depth of several thousand 
feet between perpendicular walls. The greatest of these 
cafions, that of the Colorado, is 298 miles in length, and 
its sides rise perpendicularly to a height of 5,000 or 6,000 
feet. Valleys at their commencement usually assume the 
form of amphitheatres in a degree more or less marked, 
The most regular in form are to be seen in the Central 
Pyrenees. ‘The most remarkable, on account of their 
vast dimensions and the snow-clad terraces which surround 
them, are the ow/es (boilers) of Garvarnie, Estaubé, and 
Troumouse, which the slow action of centuries has hol- 
lowed out in the calcareous sides of the mountains of 
Marboré. Undulating tracts of pasture-land furrowed 
by torrents, prodigious walls rising to 1,500 or even 2,000 
or 3,009 feet in almost perpendicular height, gigantic 
steps on which whole nations might find room to sit, 
cascades which either spread out over the precipice and 
float away in a diaphanous veil of mist, or rush down into 
the valley like an avalanche ; the high summits, glittering 
with unstained snow, which rear their heads high above 
the wall of cliffs, as if to look over the inclosure—all these 
features we find combined far in the recesses of these. 
solitary mountains, so as to render the Pyrenean amphi- 
theatre one of the grandest fab/eaux in Europe.” In the 
third division, on the circulation of water, the author 
discusses at considerable length the phenomenon of snow- 
fall on mountain heights, the successive stages through 
which the snow-field passes into the glacier form, the 
structure and phenomena of glaciers, subjects towards 
the elucidation of which Prof. Tyndall has made such 
valuable contributions. The cause of the intersec- 
tion of crevasses in glaciers is fully explained. A 
marginal crevasse, as is well known, first appears in a 
direction tending up the stream of the glacier ; it is then 
carried round by the current until it inclines in a down- 
stream direction, and is then intersected by another 
crevasse opening like the first in an up-stream direction. 
The process is repeated until the numerous intersecting — 
crevasses form a complete labyrinth. 
After several very interesting chapters upon the subject 
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Fic. 2.—Plan and section of the volcano of Rangitoto.—a Declivities of tuff ; 
4 Cone of lava : ¢ Pyramid of Scoriz. Roy 
of springs in their different varieties, the remainder of 
this division is devoted to the discussion of lakes and 
rivers, and here we find the fact carefully explained and 
illustrated that the hydrographical systems in different 
parts of the world exhibit the same relative harmony and 
order as the forms of the continents, The chapters ex- 
plaining the process of the formation of deltas, by what 
are aptly termed “ working rivers” (/leuves travailleurs), 
are especially worthy of attention, and will be found to 
contain a collection of maps and diagrams in illustra- 
tion of this branch of the subject. 
The last division, on subterranean forces, contains some 
of the most interesting chapters of the whole work, being 
devoted to the consideration of the most mysterious and 
appalling of terrestrial phenomena, namely, volcanic 
eruptions and earthquakes. Science has not yet suc- 
ceeded in establishing any definite theory respecting the 
origin of volcanic eruptions, although most valuable con- 
