64 GEOLOGY OF SW. IDAHO AND SE. OREGON. [bull. 217. 
countless herds of animals, many of gigantic size, of which our present meager fauna 
retains but a few dwarfed representatives. Noble rivers flowed through plains 
and valleys, and sea-like lakes, broader and more numerous than those the con- 
tinent now bears, diversified the scenery. Through unnumbered ages the seasons 
ran their ceaseless course, the sun rose and set, moons waxed and waned over this 
fair land, but no human eye was there to mark its beauty nor human intellect to 
control and use its exuberant fertility. Flowers opened their many-colored petals 
on meadow and hillside and filled the air with their perfumes, but only for the 
delectation of the wandering bee. Fruits ripened in the sun, but there was no 
hand there to pluck nor any speaking tongue to taste. Birds sang in the trees, 
but for no ears but their own. The surface of lake or river was whitened by no 
sail nor furrowed by any prow but the breast of the waterfowl, and the far- 
reaching shores echoed no sound but the dash of the waves and the lowing of 
the herds that slaked their thirst in the crystal waters. 
Life and beauty were everywhere, and man, the great destroyer, had not yet 
come; but not all was peace and harmony in this Arcadia. The forces of nature 
are always at war, and redundant life compels abundant death. The innumerable 
species of animals and plants had each its hereditary enemy, and the struggle of 
life was so sharp and bitter that in the lapse of ages many genera and species were 
blotted out forever. 
The herds of herbivores — which included all the genera now living on the earth's 
surface, with many strange forms long since extinct — formed the prey of car- 
nivores commensurate to these in power and numbers. The coo of the dove and 
the whistle of the quail were answered by the scream of the eagle, and the lowing 
of herds and the bleating of flocks come to the ear of the imagination mingled 
with the roar of the lion, the howl of the wolf, and the despairing cry of the 
victim. Yielding to the slow-acting but irresistible forces of nature, each in suc- 
cession of these various animal forms has disappeared, till all have passed away 
or been changed to their modern representatives, while the country they inhab- 
ited, by the upheaval of its mountains, the deepening of its valleys, the filling 
and draining of its great lakes, has become what it is. 
IGNEOUS ROCKS. 
Volcanic rocks. — The rocks which came from volcanoes are by far 
the most conspicuous of any of the formations in southwestern Idaho 
and adjacent portions of Oregon, and are apparently of greater extent 
and thickness than the associated sedimentary beds. They may, with 
sufficient accuracy for the purpose in hand, be classified as basalt and 
rhyolite, but a more critical study than has as yet been practicable 
will perhaps show that each of these divisions, and particularly the 
one here termed rhyolite, includes material that can with greater pro- 
priety be otherwise classified. 
Both the basalt and the rhyolite present two conspicuously differ- 
ent phases, due to the manner in which the material was spread out 
on the earth's surface. In each case the rock while molten was in 
part extruded by volcanoes so as to form sheets which, in many 
instances, flowed far and wide over the surface of the land before cool-, 
ing; and in part the lava while yet in the conduits cooled sufficiently 
to become rigid and was shattered by steam explosions. The frag- 
ments thus produced were blown into the air and widely distributed 
