of the westward and southward drift of the continents, accompanied by tremendous crustal deformations and concomitant widespread lava flows and great volcanic activities.
Near the close of the preceding geologic period much of the continental land was up above water, although as yet there were no mountain peaks. But as the continental land drift continued, it met with the first great obstruction on the deep floor of the Pacific. This contention of geologic forces gave impetus to the formation of the whole vast north and south mountain range extending from Alaska down through Mexico to Cape Horn.
This period thus becomes the modern mountain-building stage of geologic history. Prior to this time there were few mountain peaks, merely elevated land ridges of great width. Now the Pacific coast range was beginning to elevate, but it was located seven hundred miles west of the present shore line. The Sierras were beginning to form, their gold-bearing quartz strata being the product of lava flows of this epoch. In the eastern part of North America, Atlantic sea pressure was also working to cause land elevation.
100,000,000 years ago the North American continent and a part of Europe
were well above water. The warping of the American continents continued,
resulting in the metamorphosing of the South American Andes and in the gradual
elevation of the western plains of North America. Most of Mexico sank beneath
the sea, and the southern Atlantic encroached on the eastern coast of South
America, eventually reaching the present shore line. The Atlantic and Indian
Oceans were then about as they are today.
95,000,000 years ago the American and European land masses again began
to sink. The southern seas commenced the invasion of North America and
gradually extended northward to connect with the Arctic Ocean, constituting
the second greatest submergence of the continent. When this sea finally withdrew,
it left the continent about as it now is. Before this great submergence began,
the eastern Appalachian highlands had been almost completely worn down to
the water's level. The many colored layers of pure clay now used for the
manufacture of earthenware were laid down over the Atlantic coast regions during
this age, their average thickness being about 2,000 feet.
Great volcanic actions occurred south of the Alps and along the line of the present California coast-range mountains. The greatest crustal deformations in millions upon millions of years took place in Mexico. Great changes also occurred in Europe, Russia, Japan, and southern South America. The climate became increasingly diversified.
90,000,000 years ago the angiosperms emerged from these early Cretaceous
seas and soon overran the continents. These land plants suddenly appeared along
with fig trees, magnolias, and tulip trees. Soon after this time fig trees, breadfruit
trees, and palms overspread Europe and the western plains of North America.
No new land animals appeared.
85,000,000 years ago Bering Strait closed, shutting off the coo!ing waters
of the northern seas. Theretofore the marine life of the Atlantic-Gulf waters
and that of the Pacific Ocean had differed greatly, owing to the temperature
variations of these two bodies of water, which now became uniform.
The deposits of chalk and greensand marl give name to this period. The sedimentations of these times are variegated, consisting of chalk, shale, sand-
