STRATIGRAPHY 



315 



Cretaceous age is the physiography of the range, a record that must be 

 read in connection with the deposits from lakes and glaciers and should 

 be interpreted in the light also of the structural geology. 



The following is a tabular statement of these rocks and of the forma- 

 tions into which they are classified for the purposes of this report : 



f Eastern 

 I drift. 



Pleistocene. 



Geologic Formations represented 



f Characterized by boulders of granitic, 

 continental j gneissoid, and other Laurentide rocks ; 

 forms a moraine across Saint Mary and 

 I Belly valleys and beyond. 



[ Valley glacier drift. 



f Distinguished by absence of Laurentide 

 rocks; composed of Algonkian sedi- 



■{ mentary and igneous rocks in hetero- 

 geneous association as till and strati- 

 fied drift. 



Pleistocene or 

 Pliocene. 



Kennedy high level 

 gravels. 



f Type locality — a gravel mesa, elevation 

 5,800 feet, 5 miles east of Chief moun- 

 tain, north of Kennedy creek, and 900 

 feet above it ; characterized by water- 

 worn material of local origin, Algon- 



-{ kian rocks up to 2 feet in diameter; 

 average coarse stuff under 1 foot, much 

 of it 2 to 6 inches ; distinguished by 

 absence of glacial striae, by stratifica- 

 tion, and by altitude above present 



[, stream channels (figure 2, plate 51). 



Later Tertiary. 



TakphpHsanH marsh fClay, stratified, light gray; fine, very 

 Lake beds and maisti , homogeneous . i llte rbedded with very 



aeposits oi in ortn i friable light g ree nish sands and brown 



Fork valley. ^ lignite ; 



Earlier Tertiary. Black foot peneplain. 



Highest and oldest peneplain of the 

 Great plains in this district, cut across 

 upturned Laramie and older strata. 



Cretaceous. 



f Laramie sandstone. 



Benton shale. 



Dakota sandstone. 



[ Sandstone, hard, gray, cross-bedded, and 

 J soft shaly interbedded, carrying layers 

 of oyster shells and containing plant 

 [_ remains. 



f Shale, dark, bluish gray, very fissile, 

 ! fossiliferous, with occasional beds of 

 sandstone, medium grained, brown, 

 [_ and thin limestone layers. 



{Sandstone, yellow and brownish, and 

 shale, arenaceous, with plant remains 

 and freshwater shells. 



