444 GEOLOGICAL EXCURSION TO THE &OOKY MOUNTAINS. 



the Dakota Cretaceous, however, the transgression is more distinct, 

 •i i id that between Laramie Cretaceous and Tertiary is very marked. 

 In the area passed over during the night, after leaving the Laramie 

 exposures which form the eastern boundary of the Denver basin, Ter- 

 tiary beds extend eastward to Phillipsbnrg which is reached in the 

 early morning. From there today Center, Cretaceous beds furnish 

 the only visible outcrops, the Bed Beds of the Trias which come to the 

 surface in southern Kansas not appearing along the line of travel. The 

 coal measures of the Missouri Iowa coal basin, which also extend 

 into and are of economic importance in Kansas, pass upward into a 

 series of shales and limestones, with a tew unimportant, sheets of 

 sandstones, the whole containing a fauna of newer facies than that 

 of the uppermost members of the Carboniferous remaining in the 

 Appalachians. These have been commonly referred by local geologists 

 to the Permian, or Permo-Carboniferous. The Tertiary beds which 

 once covered the eastern portion of the plains area have been almost 

 entirely removed by erosion. They are partly replaced by the drift 

 deposits of the ice sheet, whose western margin extended a short dis- 

 tance to the west of the present valley of the Missouri river, where it 

 forms the boundary between the States of Iowa and Missouri on the 

 east and Nebraska and Kansas on the west. 



Mr. Robert Hay contributes the following on the surface geology of 

 the Plains in Kansas and Nebraska where traversed by the various 

 railroads: 



The geology of the country is substantially the same along these various routes. 

 From the longitude of about 108 80 east ward there are two formations that are 

 conspicuous. The highest I call the Plains marl. Though it has variations it is 

 remarkable for its lithologio similarity over vast areas, and samples not to be dis- 

 tinguished from each other could he obtained from the northern plains of Nebraska, 

 the midplains (Platte- Arkansas) region and the Panhandle of Texas. It is argil- 

 laceous, arenaceous, and calcareous everywhere, and its varieties are due simply to 

 the predominance of one or the other of its principal ingredients. Where the lime 

 and clay have been weathered out, sand dunes are left. It has few fossils, hut horse 

 teeth have been found in it. In at least a part of the plains it is the Bquus beds of 

 Cope. Its origin probably began in the Pliocene era and stretched all through 

 Pleistocene time. It, forms the smooth floor of the unbroken high prairie of the 

 West. The short gramma and other grasses have given its surface a compact sod 

 that turns the water oft' it and in time of storm causes rapid Hooding of the sandy 

 arroyos and river valleys. On the one hundred and second meridian and from the 

 thirty-fifth to the fortieth parallel it is from BO to L'OO feet deep, increasing in thick- 

 ness north of the Republican and decreasing eastward. Broken by the plow it 

 makes a fertile soil, and taken from excavations it is of the same quality to the 

 bottom. Vegetation has not heen sufficient to more than slightly discolor its sur- 

 face. There is no black soil on tile prairie. Owing to erosion immediately preced- 

 ing its deposition, it is found in many valleys where, vegetation having since heen 

 ranker, the marl is more humus-like under the grass roots. Erosion of the modern 



