THICKNESS OV THE MOERISON 



P>17 



feet thick; in the Owl Creek and Bighorn Mountains it is about 200 to 

 250 feet thick, and in central Montana it is less than KHi IWt thick. 

 From this it is seen to thin out toward the north. It is |)ossible, how- 

 ever, that the Kootenie may in part be equivalent to the Morrison. This 

 would reduce this northward thinning. 



Eastward from the Telluride area, the formation is about 450 feet thick 

 in the Crested Butte quadrangle, 350 feet (possibly a little more) near 

 Canon City, and 200 feet or less in the canyons in eastern Colorado. 

 There is thus a decided thinning toward the east. 



Toward the northeast, the formation is about 400 feet thick in the 

 khuaiupnicDi district, in southern Wyoming, 200 to 250 feet in the 



A 



B 



PiGDRE 2. — DidiirtniiiiiiiHi- l,'ei>res(iitalioa nf the Thickness of the Morrison Formation 



in rarioiis Areas from West to East 



A. thickness near Mack, Colorado ; P., thickness at Garden Park, near Caiion City, 

 Colorado ; C, thickness at Red Rocks Canyon, in eastern Colorado. Scale, 400 feet to 1 

 inch. 



\i(iiiity (if i^l\vllll^ and Coiuo IMutf, ami 100 feet or less around tlie 

 Hack Hills, 

 he noi'theast. 



I')!ack Hills, '['here is also, ai-eordin^' to thi.s, a decided thinning toward 



Ci;ni:i;iA Foi; i)i;ri:i;.M i xi \(i Tin-; OitiGix of tiik Formation' 



'I'lie formation is made up essentially of rine-graincrl massive materials, 

 often lefeiTcd lo as "joint-clays,'" of sandstone, sliale, a very little 

 nieilinni-graiiied conglonieiatt', and some limestone in thin beds. Many 

 of the sandstones are ai'kosic. especially those near the base of the for- 

 mation. .Man\- of the sandstones and some (d' the sn-called cdays are e.x- 

 lrem(d\ calcareons, so thai it is dillieult to decide, in some cases, whether 



