proper, where erosion has been less active on account of its distance
from the main channels of drainage. Usually, from the broken interior
edge of this slope or sedimentary plateau one descends a bluff or
escarpment, and enters the central area of slates, granite, and
quartzites, which is carved into high ridges and sharp peaks cut by many
narrow and deep valleys and ravines and generally thickly timbered with
the common pine of the Rocky Mountains. Toward the south, about Harney
Peak, the surface is peculiarly rugged and difficult to traverse. Toward
the north, also, about Terry and Custer peaks, a smaller rugged surface
appears; but in the central area between and extending west of the
Harney range is a region which is characterized by open and level parks
much lower than the surrounding peaks and ridges."

The Archæan rocks which form the core of the Hills mark the center of
the various uplifts which have attended their formation and controlled
their history. The coarse granite of Harney Peak indicating that, as the
central point of the earliest upheaval, and the three porphyries known
as rhyolite, trachyte, and phonolite, showing the uplifts of later
periods to have had their centers a little more to the north, but the
entire area is said to be only about sixty miles long and twenty-five
miles in width. It is exceptionally rough and mountainous, and
consequently has great charms for the lover of fine scenery. Erosion has
only partially denuded the peaks of the sedimentary rocks through which
they were thrust up, or by which they were overlaid during the earlier
part of several subsequent periods of submersion. The Hills, in these
remote times, led but a doubtful and precarious existence, being now an
isolated island rising out of a shallow sea, and then, owing to a
general subsidence, submerged in the ocean to so great a depth that even
Harney Peak is supposed to have almost, if not entirely, disappeared.
This up and down motion continued at intervals until the Fox Hills epoch