140 B. WILLIS—DRIFT PHENOMENA OF PUGET SOUND. 
types. The ridges of coarse, more or less stratified gravel, trending in a 
direction transverse to the ice-limit, conditioned by the slope of the land, 
and formed beneath the ice, correspond to osars.* The areas of billowy 
relief which are associated with the osars or which occur as tracts be- 
tween groups of osars are of the class of submarginal or lodge moraines. 
Vashon drift areas, interior aspects.—It is probable that the Vashon drift 
presents varied aspects in different districts. In the marginal zones the 
absence of angular or striated stones is striking. Such stones are more 
numerous on Vashon island, according to the observations of Mr Smith. 
They also occur, though in limited numbers, on Des Moines island. 
Where present they indicate that the gravels were not so vigorously 
rolled by streams, but have been carried in the lower strata of the ice. 
Farther northward, at greater distance from the margin, ice may haye 
been the principal carrier, and the till may have a correspondingly 
clayey and angular character. 
The topographic aspect of an area of Vashon till, where it has been 
spread by ice, is that of a gently undulating plain diversified by ocea- 
sional kettleholes. The ground isa gravelly loam, but within the district 
so far surveyed no extensive area of unmodified till has been observed. 
Bodies of sorted pebbles or sands and interstratified lenses of sands in 
heterogeneous gravels suggest the concurrent action of water with the 
ice in subglacial channels. 
In the northern part of Des Moines island, 6 miles (9 kilometers) west 
of Renton, is a group of round hills and short ridges worthy of note, 
The locality is. known as Sunnydale, and numerous homes are estab- 
lished there on account of the fertile soil. A central hill of oval plan 
and something over 100 feet (30 meters) high is surrounded by mounds 
and short ridges. The general arrangement trends from north to south, 
covering an oval area of about one square mile (259 hectares). On the 
north isan undulating plain of Vashon till. Southward a small stream, 
which rises in swampy hollows between the hills, pursues a relatively 
wide depression. The material composing the hills is prevailingly gravel 
and sand under a cover of sandy loam with comparatively few pebbles. 
Bodies of sand occur. On the crest of some of the ridges there is clean 
eravel. Large boulders are numerous on the surface. In the southern 
part of the area specially distinct ridges and oval hills consist of gravel 
and sand interstratified, cross-bedded, and laid with plunge structure. 
The oval hills and short ridges which make up this group appear to 
have been formed under the ice by the action of subglacial streams, 
° 
* Op. cit., p. 529. 
+ Op. cit., pp. 524, 525. 
