dilleb.] MARINE DEPOSITS. 35 
the flats about Lake Earl. Unconformably upon it (Station 5339, etc.. of Diller, 
1900) lies a Miocene sandstone replete with marine fossils, chiefly Macoma and 
Tapes. It is massive, and at the bottom where it rests upon the metamorphic 
rock it contains a multitude of waterworn pebbles, which at the base make up 
the mass of the rock and grow sparser upward. 
These Miocene layers are unconformable with No. 7, but are not horizontal; they 
are more or less arched over the irregularities of No. 7, and in the longest stretch 
observed seem to have a dip of 20° to the northward. The upper surface seemed 
more or less eroded, and upon it lie horizontally the yellow sand beds corresponding 
to No. 2 and No. 3 of the Crescent City section. I found no trace of the supposed 
Pliocene No. 4, and it may have been eroded here before the deposition of No. 2 and 
No. 3. The dikes of No. 7 do not cut the Miocene beds. Near the northwest end of 
Pebble Beach a low solid mass of fossiliferous Miocene rises 8 to 10 feet above the 
beach, capped with some nonfossiliferous, soft, sandy layers dipping 27° north and 
a little east. About 3 feet thick at the farther end, they rapidly increase eastward 
to about 1 2 feet visible above the beach, and, losing their lamination, become mas- 
sive. The Miocene is in sight only a short distance, then passes below the beach 
level, but the sand beds seem to be more or less conformable with it and are per- 
haps of nearly the same age. The latter are planed off at the top. horizontal, and 
the beds 3 and 2, above, being softer, the lower sand bed stands out like a bench 
between the Miocene point and the roadway up the bluff, at the northeast end of 
the beach. Beds No. 2 and No. 3 are the same as the beds so numbered in the 
Crescent City section, nonfossiliferous, sandy or gravelly in different proportions 
at different localities, but conformable to each other and nearly horizontal, dip- 
Sea I eve/ , 
Fig. 6.— Pebble Beach section, 2 miles north of Crescent City, Cal. 
ping slightly seaward. The sandstone below them and above the fossiliferous bed 
may perhaps be the equivalent of the Pliocene bed (No. 4) at Point St. George. 
The result of the examination of the rocks of Crescent City is to indicate for No. 
7 an unconformity with the succeeding beds formed by an eroded surface, then a 
cessation of crumpling and dike formation, then, after a depression, the deposition 
of coarse gravels shading into sandstone of Miocene age. followed by a thin Plio- 
cene layer; then another erosion period, followed by a deposit of unfossiliferous 
sand in horizontal layers, which has been moderately elevated. 
ON MAD RIVER. 
A few miles south of Crescent City the coastal plain runs out; the 
shore becomes abrupt and rocky, and so continues to beyond Trini- 
dad Head, where the broad lowland about Humboldt Bay comes in 
and at once suggests a large area of soft rocks. By the road, as this 
large coastal plain is approached, hard sandstones and dioritic and 
other igneous rocks occur here and there among the sands, gravels, 
and shell beds of the coast. Ascending Mad River beyond Blue Lake 
the alluvial plain ends abruptly at North Fork against bluffs of tilted 
sand beds locally rich in shells. These soft beds form the hills whose 
flat tops mark the ancient valley of Mad River, up which they extend 
at least as far as the mouth of Canyon Creek. A bold bluff at that 
