72 



Upper Cretaceous Seacoast in Montana [270 



few feet of thin-bedded white sandstone intervening. From 

 this and from other corroborative evidence the conclusion 

 therefore seems natural that the ridges represent the radiat- 

 ing channel sandstones of an ancient delta, which was built 

 out into the marine waters of the incipient Bearpaw sea by 

 a river of considerable size flowing from the south or south- 

 west. 



MONTANA 



Colorado 



FIG. 2. Section showing the relation of the sediments. 



PALEO GEOGRAPHIC INTERPRETATION 



Upon the basis of the foregoing data the writer draws the 

 following picture of the physiography of Judith River time. 



The low coastal plain of the mainland lay to the east of the 

 Crazy Mountains, very possibly extending thence a little 

 beyond Gibson, and upon it a gradually increasing thickness 

 of freshwater and subaerial deposits was laid down as regional 

 subsidence progressed. Simultaneously a sandy barrier beach 

 was developed and maintained in the area east of Acton, thus 

 partially shutting off a shallow embayment or lagoon whose 

 quiet waters, rendered brackish by the regional drainage, 



