The destructive agencies are so active that in a short time all
the land would disappear and be distributed over the bed of the
ocean were it not for the upheavals due to the contraction of
the crust. From causes, concerning which all geologists do not
agree, lines of weakness are developed and portions of the crust
are forced up into mountain ranges or broad plat eaus, while
other adjacent portions are de pressed. The outer rocks or those
forming the slopes of a young mountain range are composed of the
sediment of older rocks. They are the result of processes of
destruction and recon struction, which are to be at once
renewed. For no sooner are new areas exposed than the sun either
by direct heat, or through the agency of wind, frost, rain, or
running water, proceeds to carve the surface into new forms,
carrying away the waste to cover the rocks with soil for the
support of vegetation or to fill up the hol lows of the sea.
Rain not only attacks the rocks by force of impact and solution,
but by moving broken