diller] THE COASTAL PLAIN. 25 
are arable, and in some places densely forested, their tillage and 
lumbering industries furnishing occupation for the greater number 
of their inhabitants. The mountains bordering the plains on the east 
are in strong contrast to them and have a scanty population. 
For the information of those who may be interested in these small 
coastal plains as physiographic types a fuller statement is made con- 
cerning some of their features. 
The outer border is the crest of the sea cliff, which ranges from 50 
to 225 feel in height, and is illustrated in PI. IX. The el ill' is com- 
posed chiefly of soft Miocene sandstone, overlain by later deposits of 
sand and gravel, and contains near its base, as shown in the illustra- 
tion, a layer of marine shells. The soft sediments of the cliff are 
undermined by the waves of the beach and break away by their own 
weight, to be reduced to sand on the beach and spread by the under- 
tow over the adjacent sea floor in new deposits. Where hard rocks 
or gravel occur on the sea cliff and wave action is vigorous, as about 
the head of Cape Blanco, the beach is more or less gravelly. By the 
attack of the waves the sea gradually advances upon the land and 
washes away in large measure the records of its earlier work. 
The inner or landward border, which was formerly the shore line, is 
marked in places not only by a sea cliff, but by a mass of shore gravel. 
This feature is illustrated in PI. X, A, where the gravel is mined for 
gold. On the right in the distance is the ancient sea cliff at the base 
of Maddens Butte, which lias been connected with a gentler slope by 
its own talus. At its left is the coastal plain, underlain by deposits 
of gravel and sand derived from the cliff. When this coastal plain 
was formed the shore line was along the base of Maddens Butte, and 
the deposits now being mined were on the beach. The older hard 
rocks, such as form the butte and sea cliff beneath the surface soil, lie 
only a few feet beneath the gravel of the mine. 
The surface of the coastal plain is generally even, but occasionally 
has ridges of wind-blown sand from the coast, to which they are 
closely limited. The plain from Bandon to Port Orford, although 
well covered with forest or a thick growth of shrubs, is for the most 
part sandy, with many small swamp patches. Here and there, from 
the accumulation of vegetable mold or fine sediment, the soil is fertile 
and cultivated. The same is true of much of the plain north of the 
Chetco River, but south of it are large stretches of fine farming land. 
Some of the rocks are so hard as to have successfully resisted the 
attack of the waves when the coastal plain was formed and were not 
reduced to the level of the plains. They stand out as ledges on the 
plain. The most durable of the rocks encountered are of igneous 
origin, filling the chimneys of old volcanoes. Where such occur they 
stand out prominently as rock stacks upon the plain (PI. X, B). 
These are exceptional. Throughout almost the whole of the coastal 
plain the rocks have been reduced below its level and covered by a 
thin coating of sand and gravel. 
