146 B. WILLIS—DRIFT PHENOMENA OF PUGET SOUND. 
melted, came to resemble that of southern Alaska about the margin of. 
the Malaspina glacier, which Russell has so well described.* 
Such evidence of a milder climate as I have gathered is apparently 
related to deposits which accumulated during the retreat of the Admiralty 
ice and might be correlated under the head of the Admiralty epoch, but 
the stagnant ice locally lingered long after the condition of general gla- 
ciation had ceased to be, and no sharp line can be drawn between the 
glacial and interglacial epochs. So far as is now known, the latter epoch 
is not represented by deposits formed under climatic conditions indica- 
tive of an entire absence of glaciers from the region. ‘Therefore, in order 
to give the interglacial epoch definition, it is well to assign to it those 
formations which bear evidence of a milder climate, in spite of the fact 
that they also record persistence of the slowly melting ice. These are 
well represented in the Puyallup valley, and the name is therefore given 
to the interglacial epoch. The formations correlated with this epoch are 
the “ Puyallup sands” and “‘ Orting gravels” and the structure which 
will be described as the “ Tacoma delta.” By inference, though not by 
direct tracing of formations, extensive lignite beds also belong in this 
group. ; 
Pursuing the method of reading the geologic record from the more re- 
cent to the earlier episodes, it is necessary to describe formations occa- 
sioned by retreat of the Admiralty ice before having given the facts which 
demonstrate the former existence of that glacier; but the description of 
the Admiralty tili, the earlhest glacial deposit as yet recognized above sea- 
level in the Sound basin, will leave no doubt on the minds of those who 
may refer to it. I therefore take up the latest of the formations of the 
Admiralty epoch. ee 
Puyallup sands.—In a number of sections observed about the Puyallup 
valley and in one on Green river the earliest formation attributable to 
the Vashon epoch rests on an eroded surface of stratified sand. Where 
the fact of erosion is not apparent, the contact is nevertheless marked by 
the superposition of very coarse gravel and large boulders on the deposit 
of fine sand, evenly stratified. The principal occurrences observed may 
be enumerated as follows: 
In bluffs on Carbon river the coarse Douty gravels he upon the edges 
of sand beds, which are cross-stratified at a dip of 20 degrees to the south- 
west. The upper surface of the sands varies 1 to 5 feet (.8 to 1.5 meters) 
from a plane in consequence of erosion. The bed of sand is about 40 
feet (12 meters) in thickness. It is the delta of a stream which here ex- 
tended as a steep bank southwestward into quiet water. The upper sur- 
face of the sands is 600 feet (182 meters) above sea. 
* National Geographic Magazine, vol. 4, 1892, and U.S. Geological Survey, 13th Annual Report,j1892, 
ee ea 
