518 O. H. HERSHEY TERTIARY AND QUATERNARY GEOLOGY 



boulders, cobbles, pebbles, and sand grains heterogeneously distributed 

 through it; this is locally known as "white clay." 



After the ice had melted back to near the head of the valley, Deer 

 Creek eroded a broad shallow channel in the surface of the white clay 

 and floored it with stream gravel. Then in a later glacial stage the ice 

 advanced and formed a terminal moraine across the valley about 4.6 

 miles above its mouth. Above this point, on account of the high grade 

 of the valley and comparative recency of the glaciation, the creek has 

 merely cut a narrow trench into the glacial deposit. This later glacial 

 stage probably corresponds in age to the latest Wisconsin stage recog- 

 nized in the northeastern States. It is the stage whose products are so 

 pronounced throughout the western mountains. Evidences of earlier 

 glaciations are usually obscure and generally either overlooked or thrown 

 in with the phenomena of the later stage. 



Of the stream gravel below the moraine, the first 3,020 yards aver- 

 age 64 yards wide and 2 yards deep, the next 4,250 yards average 91 

 yards wide and 2 yards deep, and the remaining half mile averages about 

 100 yards wide. The first section, as evidenced by shafts, is underlaid 

 by white clay ; the distribution of the gold in it supports the idea that it 

 is of glacial origin. The last section is bordered by strips of glacial 

 material that is disposed in the form of terraces, the lower ones hum- 

 mocky and the highest one even. Probably this material was largely, 

 deposited by water beyond the end of the glacier. The older glacial de- 

 posit is certainly of considerably greater age than the deposit above the 

 moraine, but I am inclined to think it represents an early "Wisconsin 

 stage rather than a stage as old as the lowan drift sheet of the north- 

 eastern States. At any rate it is comparatively recent. 



The glacial phenomena of the Deer Creek Valley are doubtless re- 

 peated in all the valleys heading high on the eastern side of the Bitter 

 Eoot Range. There is a fine development of gravel terraces in that part 

 of the valley of the Missoula River which has the summit of the range at 

 a short distance southwest, and they are probably connected with glacia- 

 tion in the short steep gulches coming down from the high mountains. 



Glaciation in the Cceur d'Alene District^ Idaho 



In "The geology and ore deposits of the Coeur d'Alene district, 

 Idaho," ^ Mr. F. C. Calkins has briefly described the terrace gravels and 

 glacial deposits of the region, and the reader is referred to the map 

 accompanying that report for their distribution. Nearly all the peaks 



Professional Taper No. 62, U. S. Geol. Survey Pub., 1908. 



