At this epoch a wide sea, interrupted by various islands, stretched across Eurasia from Wales and western Spain to China, and spread southward over much of the Sahara.  To the west its waters were clear and on its floor the crumbled remains of foraminifers gathered in heavy accumulations of calcareous ooze,—­ the white chalk of France and England.  Sea urchins were also abundant, and sponges contributed their spicules to form nodules of flint.

The Laramie.  The closing stage of the Cretaceous was marked in North America by a slow uplift of the land.  As the interior sea gradually withdrew, the warping basins of its floor were filled with waste from the rising lands about them, and over this wide area there were spread continental deposits in fresh-water lakes like the Great Lakes of the present, in brackish estuaries, and in river plains, while occasional oscillations now and again let in the sea.  There were vast marshes in which there accumulated the larger part of the valuable coal seams of the West.  The Laramie is the coal-bearing series of the West, as the Pennsylvanian is of the eastern part of our country.

The rocky mountain deformation.  At the close of the Cretaceous we enter upon an epoch of mountain-making far more extensive than any which the continent had witnessed.  The long belt lying west of the ancient axes of the Colorado Islands and east of the Great Basin land had been an area of deposition for many ages, and in its subsiding troughs Paleozoic and Mesozoic sediments had gathered to the depth of many thousand feet.  And now from Mexico well-nigh to the Arctic Ocean this belt yielded to lateral pressure.  The Cretaceous limestones of Mexico were folded into lofty mountains.  A massive range was upfolded where the Wasatch Mountains now are, and various ranges of the Rockies in Colorado and other states were upridged.  However slowly these deformations were effected they were no doubt accompanied by world-shaking earthquakes, and it is known that volcanic eruptions took place on a magnificent scale.  Outflows of lava occurred along the Wasatch, the laccoliths of the Henry Mountains were formed, while the great masses of igneous rock which constitute the cores of the Spanish Peaks and other western mountains were thrust up amid the strata.  The high plateaus from which many of these ranges rise had not yet been uplifted, and the bases of the mountains probably stood near the level of the sea.

North America was now well-nigh completed.  The mediterranean seas which so often had occupied the heart of the land were done away with, and the continent stretched unbroken from the foot of the Sierras on the west to the Fall Line of the Atlantic coastal plain on the east.

The Mesozoic peneplain.  The immense thickness of the Mesozoic formations conveys to our minds some idea of the vast length of time involved in the slow progress of its successive ages.  The same lesson is taught as plainly by the amount of denudation which the lands suffered during the era.