THE MEDITERRANEAN NATURALIST 
101 
as regards linear expansion it is found that an in- 
crease of 14 c Far. will expand wrought iron T o«ooo 
and steel X g while, on the other hand, one ton 
in weight per square inch of section will compress 
iron and steel to the same extent. A rod of rock 
10 miles long (the thickness of our sediments) and 
and one square inch in section would weigh about 
30 tons. I am not aware of any experiments on 
the compression of rock within elastic limits having 
been made; but, for the sake of illustration, were 
the co-efficient the same for rock as wrought iron 
a rise of temperature of 420° at the bottom would 
be required to balance the vertical weight and keep 
the length intact if the rod were placed on end. 
This illustration is merely given to enable the mind 
— however imperfectly —to grasp to some extent 
the nature of the forces to be dealt with. It is thus 
seen, if the preceding proposition be granted, that 
that a time must come when the forces of expan- 
sion over come those of weight. What will then 
happen? 
Many geologists aud physicists have speculated 
upcn the effect of expansion upon the rocks of the 
earth’s crust. It is a strange fact that almost ail have 
considered only linear vertical expansion. A very 
little consideration will, however, serve to show 
that the rise of temperature of a given section of 
the earth’s crust will expand it in three directions, 
that is cubic-ally; but as the lateral expansion in 
two directions is resisted by the surrounding 
areas, the tendency is for increase of bulk to take 
place vertically, thus making the mean vertical 
rise of the whole heated area three times what 
would result from linear expansion alone. 
But, as I have pointed out in Chapter IX. of 
the “Origin of Mountain Ranges” the increase of 
bulk of the heated area would tend to dispose 
itself along lines of weakness, so that instead of 
the mass being elevated over the wdioie area it 
would rise in ridges. I have satisfied myself of 
this by experiment, but to prove it in detail here 
w r ould take too much space. Those who wish to be 
informed further had better consult the plates of 
the original work. 
The greatest internal stresses will exist in the 
base of the deposits and the original underlying 
rocks, and those subject to the overlying w r eight and 
thi enormous expansive force within them will flow 
like lead under a die. This is no fanciful statement j 
but one proved by geological investigation of the 
earth’ s crust, when it is seen that the most rigid 
rocks have been bent, folded, squeezed, lengthened 
or thickened in the most extraordinary manner. But 
in the case of old massive gneisses or complexes 
composed of igneous rocks, it has sometimes hap- 
pened that the yielding has been by shearing, where- 
by enormous masses of rock have been bodily shifted 
along fault planes, such as have lately been des - 
cribed by 'the Geological Survey as existing in 
the Highlands of Scotland. I : other cases, as in 
the Appalachians, when folding could go no fur- 
ther, shearing has taken place in the same way. 
In this manner old formations have been piled 
upon younger ones in a way to deceive the eye 
of even the practised geologist, who thought he 
was looking upon a regular and natural sequence 
of rocks. Indeed, patches of rocks have been 
bodily shifted considerable distances, and it is 
only just lately owing to the labours of many geo- 
logists that this fact has been fully recognised and 
the complicated structure of a typical mountain 
district is now in a fair way of being unravelled. 
But it will no doubt be asked how can the small 
increase of bulk caused by expansion effect such 
tremendous results? The bestanswer to the question 
is by a calculation. I set no value on statements or 
theories involving quantity unless they be reduced 
to figures, The best way to prick a scientific blad- 
der inflated by the theorist who despises numbers 
is to put it into figures. Were the author in every 
case to perform this for himself, many grand theo- 
ries would never see the light, excepting it be that 
of the fire! 
Let us consider what increase of bulk would 
ensue from the heating of an area of the earth’s 
crust, 500 miles by 500 miles, and 20 miles thick 
to a mean of 1000°, Fahr. Such a cubic mass is 
very much less than many areas which have been 
affected by sedimentation in the way already poin- 
ted out. The increase of bulk clue to expansion 
would in round numbers amount to 73,000 cubic 
miles, which is not a bad material capital to begin 
our mountain building with. 
If we allow 26,000 cubic, miles for loss by com- 
pression and in other ways we shall have 52,000 
cubic miles left for effective mountain building or 
sufficient to form a ridge of triangular section 500 
I miles long, 50 miles wide, aud 4 miles high. 
