KAME TERRACES. 135 
Hocene sandstones east of Black diamond. Northwest of the Wilderness 
are high terraces, plains of well washed gravel, and a marginal zone of the 
Vashon glacier, including a number of lakes. 
The northward trending channels differed from the present course only 
beyond the point were the river now turns from northwest to west by 
north. Thestream formerly continued northwestward. Lakes, terraces, 
and plains of washed gravel pitted with numerous kettleholes show that 
it flowed over surfaces which are 350 feet (107 meters) above its present 
level, and that the ice-barrier was near at hand. 
In this connection it is desirable to record the observations made on a 
dump of coarse gravel which occurs immediately east of Renton, where 
Cedar valley opens into Duwamish valley. From the point of the main 
plateau mass a sharp crested ridge projects 800 feet (240 meters) north- 
ward. At its junction with the slope of the plateau it is 200 feet (60 
meters) high above the bottom lands of Cedar river; where the river cuts 
a section across its northern end it is 135 feet (41 meters) high. The sec- 
tion exposes stratified gravel which dips 15 degrees to the west. ‘The 
pebbles are .5 to 3 inches (1 to 8 centimeters) in diameter, with occa- 
sional larger ones 6 to 8 inches (15 to 20 centimeters) through. An an- 
cular stone 12 inches (30 centimeters) on a side was seen. ‘he eastern 
slope of this ridge is very steep, and, with the plateau on the south, partly 
encloses a rectangular corner in the flood plain of Cedar river. The ridge 
appears to be a gravel dump from the face of a glacier which occupied 
Cedar valley. ‘he evidence of the ice in the valley indicates that the 
hollow antedated the present river. 
Washed * gravel plains.—In the interiors of the plateaus are extensive 
plains, which frequently le at lower altitudes than the marginal zones. 
The plains are strongly characterized by sterility. Scattered groups of 
small firs and stunted oaks standing in the expanse of scanty grass form 
a surprising contrast to the dense forest which prevails adjacently. The 
surface of any section of the plain is level, but successive surfaces rise by 
terrace steps toward the outer margins. The steps are from 3 feet (1 
meter) to 25 feet (8 meters) high and are strictly horizontal along their 
margins. The evenness of the surfaces is locally broken by kettleholes, or 
even by obscure ridges. ‘The material of the plains is prevailingly coarse 
gravel, sometimes washed clean, elsewhere mingled with coarse sand, 
usually stratified or cross-stratified. On the surface is a veneer of silt, 
which is filtered down among the loose pebbles beneath and forms a thin 
soil. 
* The term washed is here used in its usual English sense to modify gravel which has been swept 
to its present position by swift streams and washed clean of all clayey matrix. 
XX—Butt. Guou. Soc. Am., Vou. 9, 1897 
