On the Gulf border the Upper Cretaceous beds of Alabama and Mississippi, which were laid down in the Mississippi embayment, are in 3 stages. Below are the sands and clays of the Eutaw (300 feet) which is correlated with the Matawan of New Jersey; next follows the soft limestone, or chalk, of the Selma (500-1200 feet), and at the top are 200 to 500 feet of the Ripley sands. Eastward the water shallowed, and in Georgia we find about 1400 feet of clays and sands. Northward along the Mississippi embayment the beds thin greatly and are mostly clays and sands.

In the interior region lying upon the Dakota are the marine beds of the Colorado, of which the lower division is the Benton, a mass of shales and limestones with a maximum thickness of 1000 feet, though varying much from point to point. The depression still continuing, the sea became quite deep, making favourable conditions for the formation of the chalk and harder limestones of the Niobrara. This chalk is best seen in Kansas, but extends into South Dakota; elsewhere are sandstones and limestones with a maximum thickness of 2000 feet. A movement of reelevation of the sea-bottom began even in Colorado times, and in the northern part of the interior region oscillations of level produced alternating fresh-water, or estuarine, and marine conditions. In Montana and the Canadian province of Alberta is a thick body of estuarine or fresh-water strata with seams of coal (the Belly River formation) interposed between the marine deposits of the Colorado below and the Montana above. In Utah is another fresh-water deposit of coal-bearing rocks of Colorado age.

In the Montana epoch marine conditions still prevailed, but the waters of the northern sea had generally become much shallower, and a marked change of fauna was produced. In Alberta are coal measures of this date. Two divisions of the Montana are distinguished, although not everywhere separable; the Fort Pierre, which is composed of shales and sandstones with a maximum thickness of 8000 feet, and the Fox Hills, sandstones and some shales, which do not exceed 1000 feet. This movement of upheaval in the interior was accompanied or followed by an uplift on the Atlantic and Gulf coasts, for along these borders the uppermost Cretaceous beds are either wanting or represented by exceedingly thin deposits. In the interior the continued upheaval caused fresh-water and swampy conditions to prevail over very wide areas, though not so widely extended as had been the Upper Cretaceous sea. This great continental formation is the Laramie, which has no such eastward extension as the marine Cretaceous, but is restricted to the western side of the basin and is, in part, probably equivalent to the latest marine Cretaceous, the difference being in facies rather than in time.

However, this applies only to the older part of the Laramie, which as a formation continues much later than any of the marine stages and may even have persisted into the Eocene. The northwestern part of the continent had been converted into dry land, but a broad area of non-marine deposition extended up the course of the present Mackenzie River to62°N.lat. Another and vastly larger area began about 57°N.lat., and reached, though perhaps with interruptions, to northeastern Mexico, surrounding the Colorado island. This area was 2000 miles long and 500 miles wide, and reproduced the conditions which obtained around the Mississippi valley in the Upper Carboniferous, immense swamps and peat-bogs in which gathered the quantities of vegetable matter now converted into coal seams. The clastic rocks interstratified with the coal are probably fluviatile and lacustrine deposits, and occasional brackish-water conditions are reported from some areas. Workable coal is found in all the stages of the western Cretaceous, but none of these stages is comparable to the Laramie for the extent and thickness of its coal measures.

The Laramie was a time of tranquillity, with only slow and gentle changes of level, but towards its close some important disturbances took place, especially along the Rocky Mountains. The first of these movements affected only the Colorado island, and its effects are especially well shown in the Denver basin, where some 800 feet of conglomerates (the Arapahoe) rest upon the Laramie unconformably. The second series of movements was much more extensively felt, producing marked unconformities both in Colorado and Montana. In Colorado there was a great volcanic outburst, and the Denver stage, which overlies the Arapahoe unconformably, is principally composed of andesitic tuffs. In Montana the equivalent stage {Livingstone), which also contains considerable volcanic material, is 7000 feet thick and unconformable with the Laramie. It is probable that the Arapahoe, Denver, and Livingstone, all of which occur along the Rocky Mountains, correspond to beds which elsewhere are a part of the Laramie. The latter in eastern Wyoming passes into undoubted Eocene above, by what appears to be an unbroken continuity of sedimentation.

The Upper Cretaceous of the Pacific coast comprises the Chico series, with a maximum thickness of 4000 feet. In Vancouver's Island the Chico is coal-bearing. The faunal connections of the Chico are with southern Asia, that series having very little in common with the fossils of the interior region. The uppermost Cretaceous is wanting along the Pacific coast, except for certain coalbearing beds in Washington, which appear to represent the Laramie.

The resemblance of the Chico fossils to those of southern Asia indicates the closing of Bering Sea and thus the possibility of a migration of shoal-water animals all around the shores of the North Pacific, at the same time providing a way for the interchange of land animals and plants between North America and the Old World. The Upper Cretaceous faunas of Mexico are surprisingly different from those of the United States, and so like those of the Mediterranean region of Europe as to suggest an east and west shore-line across the Atlantic in the latitude of Brazil, while the northern connection of America with Europe probably continued also, for the shallow-water fossils of New Jersey resemble those of central Europe.

The Mesozoic era was closed in the West, as the Palaeozoic had been in the East, by a time of great mountain making, and to this movement is attributed the formation of most of the great Western mountain chains. From the Arctic Ocean to Mexico the effects of the disturbance were apparent. The Rocky Mountains, the Wasatch and Uinta ranges, the high plateaus of Utah and Arizona, and the mountains of western Texas date from this time, though subsequent movements have greatly modified them. Vast volcanic outbreaks accompanied the upheaval, which was on a far grander scale than the Appalachian revolution had been.