3io 



These features, and curved and spreading striations, indi- 

 cate the remarkable "plasticity" of ice under great pres- 

 sure. The smaller ledges have been worn into roches 

 moutonnees, and although their lea ends are usually broad 

 and craggy, they are in places smoothly polished and 

 striated. The abrasion has been greatest on the soft rocks, 

 and has left rounded ledges of the hard rocks in relief. 

 Many of the rounded points of the shore line are of this 

 nature. The general direction of movement seems to have 

 been slightly west of south. Locally, owing to the influ- 

 ence of topography, the movement appears to have varied 

 considerably from this direction. The influence of the 

 topography varied at successive stages of glaciation, and 

 as a result cross striations were produced. The direction 

 of the grooves varies only from io to 20 degrees from south, 

 but that of the striations, which frequently cross the 

 grooves and are later, varies at least from S. 50 E. to S. 

 35 W. This fact indicates that the minor topographic 

 features had little effect on the glacial movement until 

 the stage of glacial retreat. The only superficial deposit 

 formed during this period of glaciation is the Admiralty 

 till. It was doubtless more extensive than appears at 

 present, and probably furnished a large part of the material 

 of the inter-glacial deposits and, as mentioned, may occur 

 on the upland mingled with the Vashon drift. It was 

 deposited directly by ice, some of it being clearly a ground 

 moraine, but part of it was apparently deposited in water, 

 probably below sea-level. 



On the retreat of the Admiralty glaciers the land stood 

 at least 200 feet (60 m.) lower than at present, since marine 

 fossils occur in the inter-glacial deposits up to that eleva- 

 tion. Presumably the drowned pre-Glacial lowland formed 

 estuaries, and in these estuaries, under conditions of 

 comparative quiet and of moderate temperature, the May- 

 wood clays were deposited. The glaciers had not, how- 

 ever, completely disappeared from the region as the 

 irregularly distributed pebbles and large erratic glacial 

 boulders in the clays testify, since they were doubtless 

 dropped from floating ice. During the later stages of the 

 inter-glacial epoch, when the Cordova sands and gravels 

 were being deposited, either shallower water prevailed 

 or else the rivers and streams issuing from the ice front, 

 perhaps advancing at this time, were more heavily laden 

 with coarser detritus. 



