126 B. WILLIS—DRIFT PHENOMENA OF PUGET SOUND. 
Rainier, which still present fine examples of the alpine type. The north- 
ern system descended from the district of the San Juan archipelago. It 
was the southern tongue of the confluent ice-mass which, gathering on 
the Caseades in British Columbia, filled the gulf of Georgia, whence its 
main body discharged westward into the straits of Fuca. That portion 
which presumably flowed northward past Vancouver island is not con- 
sidered here. 
The southern tongue of the northern ice-mass or the northern system 
of the Puget Sound basin was far larger than the western and eastern 
systems. From the highland of the San Juan district it pushed between 
them southward beyond Tacoma and even up the Puyallup valley to 
Carbonado, where its marginal effects are to be seen at an elevation of 
1,600 feet (488 meters) above sealevel. It thus intruded into the terri- 
tory of the Rainier glaciers, which were not permitted to extend more 
than 25 miles (40 kilometers) northwest from that mountain. The over- 
powering volume of the northern ice as compared with that from the 
west and east is a fact which explains many peculiar features of the dis- 
tribution of drift and which bears directly on the origin of the topography. 
Throughout this article the name Vashon will be given to the episode 
represented by the latest occupation of the Puget Sound basin by the 
northern ice-tongue and its deposits. The term is derived from Vashon 
island, where the gravelly till characteristic of the episode occurs typ- 
ically, although not heavily. No correlation with any area beyond the 
limits of the Tacoma and Seattle quadrangles is attempted in giving this 
name, which is chosen to avoid the confusion arising from such terms as 
upper and later when comparisons with other regions become necessary. 
A lobe of the Cascade glacier opposed the Vashon glacier in the east- 
ern part of the Tacoma quadrangle. It spread a characteristic till on 
the plain on which is situated the hamlet of Osceola. This lobe of the 
Cascade glacier and its till will be accordingly designated Osceola lobe 
and Osceola till. 
The topographic features due to the Vashon Glacier system can now 
be deseribed. Those which belong to the more recent vanishing stage 
of retreat will in general be treated first, but the chronological order can- 
not be rigidly adhered to where several features of one kind developed 
during successive stages. 
Lateral moraines.—The slopes which bound the Duwamish valley on 
the east and west are steep and generally clothed with forests. Not 
having been subjected to the action of waves, they retain minor features 
which in the cutting of sea-cliffs have been obliterated along the shores 
of Admiralty inlet. These features are of glacial origin and record sey- 
eral stages of the latest glacial episode. 
