96 PRESIDENT’S ADDRESS—-SECTION C. 
formed. Or, if the flow of material still continued towards the 
same place, a mountain range on the Andean type would be the 
result. It is possible that with an elastico-viscous crust capable 
of taking a permanent set and a viscid interior, bodily tides 
might produce forced oscillations of the surface very different in 
character to the tides of a fluid body, and that slow movements 
might continue long after the exciting cause had ceased. In 
this way the irregularities in earth pulsations may possibly be 
accounted for. 
This is to some extent a return to the views of Dr. James 
Hutton, but he and his followers conceived the breaking of the 
crust to be followed by an impetuous rush of molten granite, 
carrying everything before it, and forming a mountain chain at a 
single stroke. But, in 1838, C. Darwin taught that mountain 
chains were formed, not by one enormous overflow, but by a long 
succession of small movements, each being due to the injection of 
molten rock, which became solid during the intervals; and 
this view of the injection of granite harmonises well with the 
hypothesis that the injection is due, indirectly perhaps, to bodily 
tides a few inches in height. 
Mountain ranges are said to be of all ages, and this is true in a 
sense, but not in the same sense that sediments are said to be of 
all ages. Sedimentation is always going on in some part of the 
globe : it is a continuous phenomenon, as also is oscillation of the 
surface. But mountain building shows a kind of periodicity. 
Mountains are produced at certain periods which alternate with 
longer intervals of comparative repose, these intervals being of 
unequal length. This has always been recognised by geologists, 
and in the early days gave rise to the hypothesis of catastrophes. 
When advancing knowledge showed the incorrectness of general 
catastrophes, the uniformitarian doctrine came to be believed, 
and the periodic movements of the crust were put down to the 
shrinking of a cooling nucleus ; they were no longer catastrophes, 
but paroxysms. This explanation disappears with the contraction 
theory, but the fact of periodicity in certain earth movements 
still remains, although the paroxysms are now regarded as relative 
and not absolute or sudden. These periods of relative paroxysmic 
movement by the theory now under discussion are due chiefly to 
periodic weakenings of the crust in different places caused by the 
accumulation of sediments, which thus allow the outflow of 
currents of a fluid interior. 
Sir H. De la Beche, in 1834, pointed out how the association 
of granite with contorted rocks is so common that there must be 
something connected with the former which has had an influence 
on the latter. The injection of a large mass of molten matter 
would, he said, produce a state of things favourable to contortion, 
but if the intruding mass was more solid the conditions would be 
still more favourable, and, he continued, we can readily conceive 
