JUAN DE FUCA LOBE OF CORDILLERAN ICE SHEET 337 



a tidewater front from a point east of Cape Beale on Vancouver 

 Island to Cape Johnson on the Olympic Peninsula, a distance of 

 about 60 miles. Only Greenland and Antarctica today possess 

 tidewater glaciers of comparable extent. Figure i shows the 

 proportions of this lobe and the probable greater deployment at 

 the mouth of the strait, along which the greatest movement of ice 

 doubtless occurred. 



The wastage of the Juan de Fuca Glacier was largely by bergs, 

 notably in contrast with that of the glacier of Puget Sound which 

 terminated at its maximum wholly on a land surface. Only the 

 southern margin of the Juan de Fuca Glacier terminated on the 

 land, and only in such a situation could outwash deposits be made 

 at the maximum extent of the ice. 



The area invaded by the southern portion of the Juan de Fuca 

 Glacier is drained by Quillayute River. This stream and its tribu- 

 taries on the coastal plain flow through young valleys cut some 

 50 feet into a great valley train which extends from Forks to the 

 ocean. At Mora, the altitude of the surface of the valley train is 

 about 30 feet above tide. 



At Forks Prairie on the valley train, the gravel is more than 100 

 feet deep, and wells drilled here have encountered many large 

 bowlders distributed throughout the gravel. Quillayute Prairie, 

 between Forks and Mora, is an isolated plateau-like portion, a few 

 square miles in area and from 75 to 135 feet above the surface of the 

 surrounding plain. It is composed of gravel but has an irregular 

 surface in its northeastern part, strongly suggestive of the pres- 

 ence of blocks of ice during its building. Its isolated position 

 apparently is the result of dissection of an earlier valley train of 

 which it is a portion. From the evidence of the irregular topogra- 

 phy in the northeastern portion, the terminal margin of Juan de 

 Fuca Glacier is here mapped as reaching Quillayute Prairie. 



A valley train extends down the Soleduck Valley from the base 

 of the Olympic Mountains and joins this broader tract beyond the 

 hmits reached by the glacier. The gravel of which it is composed 

 is dark in color, and was derived largely from basaltic rocks and 

 dark-colored sedimentaries. This is typical of most of the debris 

 from this portion of the Olympic Mountains. But scattered 



