324 GEOLOGICAL EXCURSION TO THE ROCKY MOUNTAINS. 



gifted and picturesque, and dotted over by isolated buttes and long 



ridges of low hills, sculptured forms left by erosion. 



The railroad crosses the boundary line between the States of Dakota 

 and .Montana just west of Sentinel Butte station. Sentinel Pntte lies 

 a few miles south ot the railroad and is plainly visible to the tourist. 

 standing out upon the plain a most impressive object, like a monument 

 on the desert. Geologically, it presents much of interest, as its base 

 is composed of the upper beds of the Laramie, and it is capped by con- 

 formable strata of fresh-water deposits regarded as of early Kocene 

 age. 



The railroad reaches the Yellowstone valley at Glendive, and from 

 here it follows the river all the way to Livingston, a distance of 340 

 miles (547 km.), with a gradual ascent of over 2,200 feet. The valley 

 between the bluffs varies from l to Smiles in width, the river mean- 

 dering from side to side. Several large tributaries to the Yellowstone 

 which enter the river from the south are crossed, including Powder 

 river. Big Horn, Clarks Fork, and Stillwater. The first named rises 

 between the Black Hills and the Big Horn mountains; the second 

 drains the Big Horn mountains; and Clarks Pork and the Stillwater 

 have their source in the Absaroka range. The railroad crosses the 

 river three times, and for the greater pari of the distance follows along 

 under the blntl'son the south side. The Yellowstone valley above the 

 bluffs presents much the same physical features as seen in eastern 

 Montana, and the geological features offer but little in the way of change 

 to break the dull monotony. The bluffs and low-rolling hills are formed 

 of yellow sandstone, for the most part horizontal. It is the prevailing 

 color of these beds that has given the name to the river, and conse- 

 quently to the now famous Yellowstone Park, where the river has its 

 source. 



From Glendive, blutfs of Laramie sandstone maybe seen stretching 

 far down the valley, which has here a northeasterly direction. About 

 10 miles (10 km.) above Glendive, at the foot of the bluff on the east 

 side of the valley, occurs an exposure of Fox Hills beds. These beds 

 are determined by their organic remains, but are difficult to recognize, 

 as Histologically they are similar to the overlying Laramie, and both 

 series are conformable. There is exposed here the base of the Laramie, 

 whereas the top of the series occurs at. Sentinel Butte. According to 

 Dr. 0. A. White the thickness of the Laramie in western Dakota and 

 eastern Montana is nearly 3,000 feet (014 km.). 



Shortly after leaving Miles City the lignite beds crop out at tie* base 

 of the Laramie; and at Howard, Fox Hill strata are said to come to the 

 surface from beneath the overlying Laramie, but they are by no means 

 easily distinguished. 



At Billings the first important exposure of Middle Cretaceous is 



