Bibliographical Notices. 259 



The relative positions, range, and thickness of these formations 

 are well illustrated by maps and sections : the geography and 

 geology of the region beiug shown in plates i. & ii. and ix. to xi , 

 xxxvii. & xxxviii.; physical features being richly represented 

 by numerous figures in the text and in plates. 



The AUuvium is chiefly noticeable in the valleys, particularly in 

 that of the Platte and its tributaries. The " Ureat Sand-hill 

 district," in Central Nebaslia (of 24,000 square miles), is composed 

 of wind-borne sand largely derived from the Arikaree formation. 

 Wide plains of Loess occupy nearly one third of Nebraska, and 

 cjnsist largely of Boulder-clay. The Ogalalla beds consist ol 

 calcareous grit and pebbles ; and they have formed gravel when 

 disintegrated. The Arikaree formation (about 430 feet) of sand 

 and concretions, with conglomerate at base, contains also volcanic 

 ash, and yields abundance of the curious Dcemondice or " Devil's 

 Corkscrews." The concretions are frequently tubular, and there 

 are channels in the sand filled with conglumerate. This formation 

 Aveathers into the frequent upstanding and isolated pinnacles, stacks, 

 chimneys, as well as butts and blufts, forming remarkable and 

 picturesque features in the region, as shown in many of the plates 

 and figures. The Gering Sandstone varies considerably in thickness 

 and in colour and hardness, and has conglomerate at the base. 



The hard pinkish Brule Clay is about 600 feet thick, thinning 

 eastwards. Then greenish sandy clay (Chadron formation) follows 

 below, and is said to have yielded remains of Titanotlierium. 



Equivalents of the Laramie formation, extending for some way 

 under South-western Nebraska, are sandstone and clay. The 

 Pierre Clay, under the central-western part of the State, is at least 

 2000 feet thick. The Niobrara Chalky limestones and the Benton 

 Shales are 450 feet thick to the east and thicker to the west. The 

 Dakota Sandstone (with a basal Lower Cretaceous sandstone), about 

 400 feet thick, underlies nearly all Nebraska. " This formation 

 carries the great artesian-water supplies, which are so extensively 

 developed by wells in eastern South Dakota, and on low lands in 

 Knox, Cedar, and Boyd counties, Nebraska " (page 9). 



Volcanic ash constitutes two widespread beds in the Brule Clay, 

 some limited and some thick beds in the Gering formation, and a 

 general admixture as well as several thick beds in the Arikaree. It 

 is rare in the Ogalalla, and it occurs in the lower portion of the 

 Loess in the central and western parts of the State. The ash was 

 probably blown over from volcanoes in the Kocky Mountains (pages 

 42 & 43). 



Carbonifei'ous limestones, shales, and sandstones underlie all 

 Nebraska. The Cottonwood FusuUna limestone has been recognized. 

 In the south-eastern corner of the State the sinkings have proved 

 about 1200 feet, of which 200 is Permian. 



At Lincoln the Lower Limestones (partly Devonian) are at 1635 

 feet ; then Trenton Limestone to 1947. Then follow magnesian 

 limestones 143 feet, then red sandstone (Cambrian) and red 

 quartzite (Alongian, pierced for 270 feet), resting on granite. 



