OPINIONS OF VOLTAIRE AND LAPLACE REGARDING GEOLOGY. 321 
for it is not consonant with the catastrophic ideas which pre- 
vailed so late in this century. It was certainly a foreshadowing 
of the opinions of the advanced school of the present day, 
which denies that any palpable amount of temperature has 
existed at the surface, conducted from below, since life has 
been in the sea and on the land ; and which asserts that the hot 
spring, the volcano, and the measurable heat in mines represent 
so much available kinetic energy, the result of rock move- 
ment and earth contraction. The primary energy bears a very 
slight relation to the size of the globe and has not been exerted 
on a grand scale since the present density has existed. The 
exceeding slowness of the great crust movements appears to have 
been in relation to the comparatively small depth of surface 
affected by them. Laplace does not indicate the depth impli- 
cated beneath the surface in the successive movements which 
we may assume so altered the aspect of nature as to originate and 
terminate physical geographies of old — geological formations : 
but it may be now assumed that the movements must have 
diminished in intensity from the surface downwards, and that 
their sum total since the laying down of the Laurentian sedi- 
ments has been vast. There is a proof of this which has not 
been much considered. Endeavour, in the mind’s eye, to 
flatten out the curvatures of the strata of the Himalayas and 
Alps, and of the Continent to the north and south, treat the 
curvatures of the Scandinavian hills, the Oural and the Andes, 
in the same manner, and consider the vast space once occupied 
by the horizontal strata. Do the same in respect to mining 
districts, from off which Mountains have been worn and washed 
away, and extend their folded and contorted strata, in the 
imagination, until they represent the breadth and length of their 
original deposition. There are no vast, gaping fissures, but, 
with the exception of some few lands, every part of the great con- 
tinent is formed by sub-rock which once, before it was exposed to 
tangential thrust and curved, covered at least twice its present 
area. I know of no other subject in relation to geology, which im- 
presses the mind so much regarding the secular contraction of 
the globe, since the first appearance of life. Laplace insists 
that the earth was primitively fluid, and that the present 
shape of the surface of the earth, covered more or less as it is 
by sea, is in accordance with the laws of equilibrium, a slight 
deformity only existing. He then proceeds to prove that the 
density of the layers of the earth increases from the surface to 
the centre, and that these layers are nearly regularly ar- 
ranged around the centre of gravity. All this led up, in after 
years, to the knowledge that the density of the earth is greatest 
under the ocean, and least imder the mountain-chains, that 
of the plains being intermediate ; and also that the centres of 
figure and of gravity do not correspond. 
