DELTAS AT HIGH LEVELS. 131 
of the terrace are not regular, but exhibit inequalities of level of 10 to 40 
feet (3 to 13 meters). A short distance back from the margin, however, 
the surface becomes an even plain, with gentle northern slope, and ex- 
tends to the south and southeast with monotonous character for from 
2 to 4 miles (3 to 6 kilometers). Near its northern margin this terrace is 
composed of sand and fine gravel, which are stratified. Further south 
the gravel gradually increases in proportion and boulders up to 1 foot (.8 
meter) in diameter appear upon it. The materials, the terraced form, 
and the stratified structure identify this feature as a delta formed by 
streams flowing in from the southeast and south. The relations to ex- 
isting drainage indicate that the delta is a composite one, derived from 
the older representative of White river and the corresponding ancestor 
of Carbon river, and the delta plain is divided north and south by a 
slight swampy depression which marks the limits between the two river 
deposits. 
The body of water in which these deltas formed could have been re- 
tained only by an extensive ice-front on the north. The delta sands and 
the marginal features of the Vashon glacier during retreat both rest upon 
the till surface of the eastern glacier, and may be correlated with a strong 
degree of probability. 
Six miles south of the front of this delta is a similar terrace at a higher 
level, which belongs to an earlier stage of the Vashon ice advance. It 
forms the plain north of Carbonado. On the road from South Prairie to 
Carbonado, 1.5 miles (2.4 kilometers) north of the latter town, a steep 
bank, 200 feet (60 meters) high, occurs. This bank is composed of brown 
sands, which are incoherent when dry and are generally of uniform char- 
acter and interstratified with some layers of fine gravel. The summit of 
the terrace forms a nearly level plain, which is bounded by the deep 
canyon of Carbon river on the west, by its terrace front on the north, 
and by a deep ravine on the east. As in the previous case, the mate- 
rials, the structure, and the form are all characteristic of a delta, which 
can, without question, be attributed to Carbon river. The elevation of 
this terraced front is 1,080 feet (829 meters) above sea. 
A little more than 2 miles (3 kilometers) further south, among the 
foothills of mount Rainier, is a swampy level whose elevation is 1,600 
feet (488 meters) above sea. Its area is about one square mile (2,589 
square meters), and it les against slopes carved in the Hocene coal meas- 
ures. Along its eastern side, at the foot of the mountain slope, is the 
shallow channel of Flett creek. On the west is the canyon of Carbon 
river, 500 feet (150 meters) deep. The soil of this level is a sandy loam, 
and its northwestern front isa terraced slope about 350 feet (100 meters) 
high. The structure of the deposit is not exposed, and it is densely cov- 
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