26 
ELEMENTS OE GEOLOGY. 
ing proofs that the external parts of the earth were not all 
produced in the beginning of things in the state in which 
we now behold them, nor in an instant of time. On the con¬ 
trary, he can show that they have acquired their actual con¬ 
figuration and condition gradually, under a great variety of 
circumstances, and at successive periods, during each of which 
distinct races of living beings have flourished on the land 
and in the waters, the remains of these creatures still lying 
buried in the crust of the earth. 
By the earth’s crust,” is meant that small portion of the 
exterior of our planet which is accessible to human observa¬ 
tion. It comprises not merely all of which the structure is 
laid open in mountain precipices, or in cliffs overhanging a 
river or the sea, or whatever the miner may reveal in arti¬ 
ficial excavations; but the whole of that outer covering of 
the planet, on which we are enabled to reason by observa¬ 
tions made at or near the surface. These reasonings may 
extend to a depth of several miles, perhaps ten miles; and 
even then it may be said, that such a thickness is no more 
than 4^ part of the distance from the surface to the centre. 
The remark is just: but although the dimensions of such a 
crust are, in truth, insignificant when compared to the entire 
globe, yet they are vast, and of magnificent extent in relation 
to man, and to the organic beings which people our globe. 
Referring to this standard of magnitude, the geologist may 
admire the ample limits of his domain, and admit, at the same 
time, that not only the exterior of the planet, but the entire 
earth, is but an atom in the midst of the countless worlds 
surveyed by the astronomer. 
The materials of this crust are not thrown together con¬ 
fusedly ; but distinct mineral masses, called rocks, are found 
to occupy definite spaces, and to exhibit a certain order of 
arrangement. The term rock is applied indiflerently by ge¬ 
ologists to all these substances, whether they be soft or stony, 
for clay and sand are included in the term, and some have 
even brought peat under this denomination. Our old writers 
endeavored ^o avoid offering such violence to our language, 
by speaking of the component materials of the earth as con¬ 
sisting of rocks and mils. But there is often so insensible a 
passage from a soft and incoherent state to that of stone, 
that geologists of all countries have found it indispensable to 
have one technical term to include both, and in this sense we 
find Todie applied in French, rocea in Italian, and felsart in 
German. The beginner, however, must constantly bear in 
mind that the term rock by no means implies that a mineral 
mass is in an indurated or stony condition. 
