176 ALASKAN MINERAL RESOURCES IN 1904. |bull. 259j 
from 100 to 200 feet high, which has been traced southeastward for 
about 15 miles, giving a definite key to the stratigraphy of a portion of 
the field. 
The thickness of the Corwin formation exposed along the coast near 
Corwin Bluff is not less than 15,000 feet. The base of the formation 
has not been observed, but it probably rests unconformably on the 
Paleozoic rocks. 
Fossil plants collected from it indicate that the age is Jurassic. 
The structure consists of several broad synclines and anticlines, the 
dips of the beds varying from 0° to 60°. There is no evidence of 
faulting other than minor shearing movements parallel with the 
bedding planes. 
The Corwin formation is conformably overlain by a more arenaceous 
series of sandstones and shales in which neither coal beds nor fossils 
have been found. The contact of these rocks with the Corwin rocks 
may be seen about 2 miles west of Corwin Bluff, whence it extends 
southeastward for several miles to the limit of the area investigated. 
The western limit of the formation is a well-defined fault line extending 
southeastward from a point on the coast 3 miles east of Cape Lisburne, 
where the formation is in contact with the Paleozoic, which is over-f 
thrust. The structure of this formation increases in complexity from 
its base at the top of the Corwin formation as this fault is approached; 
there are intense crumpling and numerous minor thrust faults. For 
this reason it is impossible to estimate the thickness of the formation, 
but the evidence obtained indicates that its minimum thickness is not 
less than 5,000 feet. 
QUATERNARY FORMATIONS. 
Pleistocene and Recent deposits of gravel, sand, silt, and ground ice 
occur at a number of places in the region, the largest area being about 
88 square miles in the Point Hope foreland, already described. A 
part of this area is said to be underlain b}^ ground ice. 
Smaller Quaternary deposits occur near the mouth of Thetis Creek, 
at Cape Sabine, at Cape Beaufort, and in the valley of the Pitmegea 
River. 
Where such deposits occur along the coast, cliffs are formed by the 
undercutting of the surf, in which ground ice is often exposed beneath 
beds of peat, silt, or talus from the higher hills. 
DETAILED DESCRIPTION OF THE COAL FIELDS. 
MESOZOIC COAL FIELD. 
Geology, topography, and extent. — The Mesozoic coal-bearing forma- 
tion, described on page 175, outcrops along the coast from a point 26 
miles east of Cape Lisburne eastward for 40 miles to Cape Beaufort, 
beyond which point the hills recede from the coast. The formation 
