202 GEOLOGY. 



less mixed with calcareous deposits, which were derived mainly 

 from a land mass that was raised up at the close of the Carbonifer- 

 ous, and extended from the Wasatch west of the meridian of 117 

 30' for 200 miles westward, and for an unknown distance north and 

 south. (King.) The materials of this land mass were mainly silic- 

 ious, and fully seven-tenths of the deposits that constitute these 

 cretaceous rocks came from their disintegration and erosion. At 

 the close of each epoch represented by these groups, the shore line 

 of the old interior cretaceous ocean retreated farther to the west and 

 northwest. By the time the Laramie epoch was reached, it was> 

 during much of the time, only a vast marsh or bog, full, no doubt,, 

 of low islands, and subjected often to incursions from the sea, and 

 again constituting an estuary, and occasionally even becoming a 

 fresh water lake. All this is evident from its vegetable and animal 

 remains, which sometimes are marine, sometimes land, and some- 

 times of brackish and fresh water types. From the Triassic to the 

 Cretaceous, and through its groups to the upper boundary of the 

 Fox Hills, only marine forms are found, except in a very few in- 

 stances where a few fresh water species exist underlaid and over- 

 laid by a true cretaceous fauna. 



The materials of this Laramie Group are, like the preceding,, 

 principally sandstones, but varying a great deal more in litho- 

 graphic character in different sections. Intercalated with the sand- 

 stones, at various horizons, are clayey and shaly layers, and a few 

 beds of pure clay, and many strata of carbonaceous shales. The 

 principal colors are buff, pink, red and various shades of yellow* 

 Sometimes the dip is slightly east or west, or even entirely horizon- 

 tal. Its undulations are wave like, and the inclination of the flanks 

 are always under 5 or 6. (Clarence King.) The thickness of this 

 series of beds ranges from 1,500 to 5,000 feet. 



This group can be studied to great advantage at the exposures 

 along the railroad east of Separation station, where colored sand- 

 stones, some clayey beds, and a number of coal seams, leaf impres- 

 sions and carbonized stems are found, and often exposed. No- 

 where, however, is it seen on a grander scale than in the Upper 

 Missouri, where it was first noticed and reported on by Lew r is and 

 Clarke, as early as 1804. From a Mandan village on the Missouri,, 

 they traced these lignitic measures to the Yellowstone, and for a 

 great distance along this river. The length of these measures, as 

 observed by these explorers, was over six hundred miles. After- 



