AMERICAN 48 1 



called marl. The Appalachian Mountains, which had been sub- 

 jected to the long-continued denudation of Triassic, Jurassic, and 

 Lower Cretaceous times, were now reduced nearly to base-level, 

 the Kittatinny plain of geographers (see p. 342). This peneplain 

 was low and flat, covering the whole Appalachian region, and the 

 only high hills upon it were the mountains of western North Caro- 

 lina, then much lower than now. Across this low plain the Dela- 

 ware, Susquehanna, and Potomac must have held very much their 

 present courses, meandering through alluvial flats. 



On the Gulf border the Upper Cretaceous beds of Alabama and 

 Mississippi are limestones called the Rotten Limestone below (500 

 to 1200 feet thick), and the Ripley above (200 feet). 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 Be?ito?i, 

 a mass of shales and limestones with a maximum thickness of 

 1000 feet, though varying much from point to point. The depres- 

 sion 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 stage marine conditions still prevailed, but the 

 waters of the northern sea had generally become much shallower, 

 and a marked change of faunans produced. In Alberta are coal 

 measures of this date. Two divisions of the Montana are distin- 



