478 KEMP AND BILLINGSLEY SWEET GRASS HILLS, MONTANA 



1. The extent of Jurassic uucuiit'orinity and ei'o.sioii. 



2. The character of the Mowry-Thermopolis phases of the Colorado 

 and the western edge of the Thermopolis "trough" of black shale deposits. 



3. The thickness and character of Upper Colorado. 



4. The shoreline of the Claggett Sea in this region. 



The first two of these facts are of great imjiortance in the exploration 

 for oil; the last two are of interest as adding fixed points to the general 

 knowledge of the Cretaceous history of the northern plains region. 



GLACIAL DRIFT 



The plains around the three buttes are abundantly mantled with 

 glacial drift. Transported boulders are frequent and are chieiiy Pre- 

 cambrian rocks from the main range of the Eocky Mountains, 100 miles 

 to the west. The drift lies with an irregular surface, and in its inequali- 

 ties are small ponds in the area to the east of West Butte. 



