216 THE BEAUTIES OF NATURE CHAP, 
with ridges. Or again, if we place some sheets 
of paper between two weights on a table, and 
then bring the weights nearer together, the 
_ paper will be crumpled up. 
In the same way let us take a section of 
the earth’s surface AB (Fig. 17), and suppose 
that, by the gradual cooling and consequent 
contraction of the mass, AB sinks to A’B’, 
A B 
‘RB’ 
. A IB" 
A’ % 
Fa B 
Fig. 17.— Adapted from Ball’s paper ‘‘ On the Formation of Alpine Valleys 
. and Lakes,” Lond. and Ed. Phil, Mag. 1863, p. 96. 
then to A”B”, and finally to A”B”. Of 
course if the cooling of the surface and of the 
deeper portion were the same, then the strata 
between A and B would themselves contract, 
and might consequently still form a regular 
curve between A” and B”. As a matter of 
fact, however, the strata at the surface of our 
globe have long since approached a constant 
temperature. Under these circumstances 
there would be no contraction of the strata 
between A and B corresponding to that of — 
a 
Basie Nie nye 
