722 G. SHERBURNE ROGERS 
brown by iron oxide, and the shale may have been derived from 
nearly any kind of an igneous rock. Three of the sections were 
made from the grayish sandy lenticular material mentioned above, 
collected at two places about 10 miles apart in T. 9 N., Rs. 42 and 
43 E. They are all decidedly tuffaceous in character and contain 
about 50 per cent of angular, subangular and rounded fragments of 
a brown volcanic glass, commonly more or less devitrified and 
altered. Quartz in small angular grains makes up about 4o per 
cent, and the remainder consists chiefly of kaolin and chlorite. 
Fic. 4.—Cross-bedding in white sandy clay facies of the Lebo shale member, sec. 
30, T. 11 N., R. 49 E., P.M., Montana. 
Though the quartz indicates a considerable admixture of foreign 
material, this would be expected at a distance of 175 miles from the 
supposed source. One slide was made from a fine-grained, sandy, 
yellow-gray bed; this also revealed the presence of some volcanic 
glass, but the rock consisted chiefly of very small fragments of 
chloritic material with considerable quartz. Finally two sections 
of sandy shale partially baked by the action of a burning coal bed 
were examined. ‘Their original character was, of course, largely 
destroyed, but fragments of a fresh green augite were identified in 
both of them. These descriptions hold also for the slides prepared 
