159
in a diagram (Fig. 9) in which we eliminate intermediate
conditions, and regard the early and final stages of development
only. In the upper sketch we suppose the lateral compression much
developed and the upward movement of the geotherms in progress.
The dotted line may be assumed to be a geotherm having a
temperature of viscosity. If the conditions here shown persist
{Fig. 9}
indefinitely, there is no doubt that the only further
developments possible are the continued crushing of the sediments
and the bodily displacement of the whole mass to the north. The
second figure is intended to show in what manner these results
are evaded. The geotherm of viscosity has risen. All above it is
affected mechanically by the continuing stress, and borne
northwards in varying
160
degree depending upon the rigidity. The folds have been
overthrown and drawn out; those which lay originally most to the
south have become the uppermost; and, experiencing the maximum
amount of displacement, overlap those lying beneath. There has
also been a certain amount of upthrow owing to the hydrostatic
pressure. This last-mentioned element of the phenomena is of
highly indeterminate character, for we know not the limits to
which the hydrostatic pressure may be transmitted, and where it
may most readily find relief. While, according to some of the
published sections, the uplifting force would seem to have
influenced the final results of the orogenic movements, a
discussion of its effects would not be profitable.
161