46 PETKOLEUM OF PACIFIC COAST OF ALASKA. [bull. 250. 
rock cliffs (igneous rock, bedded, as on south shore of the bay), while 
the others are composed of angular fragments of the same rock. The 
more easterly ones are all of the latter kind. 
The most easterly of the rock cliffs shows the following section : 
Section on north shore of Chinitna Bay. 
Feet. 
Conglomerate with interbedded shale and sandstone, the last two carrying 
fossil sticks and fragmentary leaf impressions 15 
Dark-gray shale, with upright tree trunks 20 
The strata here are almost or quite horizontal. The trees are 
between 1 and 2 feet in diameter, are silicified, and show the structure 
of the wood very distinctly, while numerous small sticks lie in the 
bedding of the shale. The leaves are Tertiary species. 
STRUCTURE. 
The structure of this region consists of a broad, low, somewhat 
undulating anticline parallel to the shore of Cook Inlet and to the 
general line of the eastern front of the Chigmit Mountains, followed 
on the west by a narrow syncline, beyond which is a second very 
closely folded and probably faulted anticline. The dip in the broad 
easternmost anticline is moderate in amount and very regular, except 
on the crest of the fold, where it is undulating, but not in excess of 
10°. On the eastern limb the dip varies from 20° to 28°, diminishing 
as the shore is approached, and on some of the long points and islands 
becoming almost or quite horizontal. The steepest dip in the south- 
western part of the field was observed on the shore of Enochkin Bay, 
where the rocks are inclined southeastward at an angle of 28°. The 
greatest dip at the northern end of the field is betw T een half a mile and 
a mile southeast of the entrance to Chinitna Bay, where it varies from 
25° to 45° SE. On the western flank of this anticline the dip is 
about 17°. 
The nature of the undulations at the crest can be seen in the cliffs 
on the eastern side of Enochkin Bay. The dip is southeastward for 
the first 4 miles above the mouth of the bay, measured along the shore 
and averages about 20°. There is then a low anticline at the mouth 
of a small creek, 4 miles above the entrance to the bay and half a mil 
below the lower cabin, which is situated at the end of the wagon roac I 
to Oil Bay. A small syncline is crossed at the lower cabin or jus | 
below it. The dip is southeastward for about 2,000 feet along th< j 
shore above the cabin, where the rocks bend over the top of anothe:] 
low anticline and dip to the northwest. Just below this point a fault 
with a displacement of at least 25 feet, extends into the cliff at righ 
angles to the shore. The fault plane is perpendicular to the bedding jj 
which clips 10° SE. A crevice G feet wide is opened along the faul 
