2o8 The American Geologist. October, i904. 
fication, lo to 20 or 30 feet thick, forming- the surface of the 
plateau, inclosing rather scanty small rock fragments, with a 
few large boulders. Good sections of the successive deposits 
are seen in the sea cliffs at and south, of the ferry landing, 
and likewise on the west side of the plateau ; and they all seem 
to me referable to the time of the final melting of the ice lobe, 
being modified drift with a surface of till. 
Most of the area of Seattle city has till on the surface, 
which rises in very massive, smoothly rounded hills, 250 to 400 
feet high. Here, and in the northern suburbs, about lake 
Union and Green lake, the till has nearly the same very com- 
pact and clayey texture, and the same considerable proportion 
of small stones and large boulders, as the average till of south- 
ern and western Minnesota ; but it has much fewer boulders 
than are common in the till of northeastern Minnesota and gen- , 
erally thence east to New England. 
Sections cutting through the till on Washington street, two 
blocks southwest of the court house, at the bight of about 
150 to 175 feet above the sound, shpw it to have there a thick- 
ness of only 2 tO' 8 feet along a distance of about 250 feet, being 
underlain by light gray, finely laminated shales, which seem to 
me probably of Lower Tertiary age, like the lignite-bearing 
shales in the vicinity of Renton, near the south end of lake 
Washington, about ten miles south-southeast of Seattle. 
Numerous other sections in this city show the glacial and 
modified drift to be frecjuently no more than 10 to 25 or 40 feet 
thick, with such shales lying beneath and reaching to an un- 
determined depth. 
The massive hills were subaerially sculptured in the shales 
before the Ice age, and are only thjinly veneered with the drift ; 
but in the valleys the drift doubtless attains, m some places, a 
much greater thickness. For example, we cannot doubt that 
the long north to south valley occupied by lake Washington, 
whose water surface is 22 feet above the sound and the sea, 
with a maximum depth of 222 feet, had, along some route now 
filled l)y the drift, a continuous preglacial connection, nowhere 
less than 200 feet deep below the present sea level, joining 
the lake valley with that of the sound. 
Within the third of a mile eastward from Renton to a brick- 
yard, which uses the Tertiary shales, the blufif rising at the 
