These hills have their summits apparently cut off
about the same elevation, so as to leave flat surfaces at top. It
is conjectured by some that the whole country may originally have
been of the altitude of these tabular hills; but through some
process of nature may have sunk to its present level; these
insulated eminences being protected by broad foundations of solid
rock.
Captain Bonneville mentions another geological phenomenon north
of Red River, where the surface of the earth, in considerable
tracts of country, is covered with broad slabs of sandstone,
having the form and position of grave-stones, and looking as if
they had been forced up by some subterranean agitation. "The
resemblance," says he, "which these very remarkable spots have in
many places to old church-yards is curious in the extreme. One
might almost fancy himself among the tombs of the pre-Adamites."
On the 2d of June, they arrived on the main stream of the
Nebraska or Platte River; twenty-five miles below the head of the
Great Island. The low banks of this river give it an appearance
of great width. Captain Bonneville measured it in one place, and
found it twenty-two hundred yards from bank to bank. Its depth
was from three to six feet, the bottom full of quicksands.
