PETROLEUM AT CONTROLLER BAY. 93 
^presence of petroleum in rocks of this character is somewhat unusual 
and worthy of notice. Similar occurrences of small quantities of oil 
In metamorphic rocks are known in California and Washington, where 
the oil is considered to have migrated into the metamorphic rocks 
Subsequent to their alteration. A similar explanation may account 
for the Alaska occurrence. The writer would suggest as a possible 
(explanation that the metamorphic rocks, which are known to be sepa- 
rated from the Tertiary shales by a fault, are overthrust upon the 
shales along a fault plane of low hade, and that the oil at the seepages 
iwest of Ragged Mountain is coming through the metamorphic rocks 
from underlying shales. 
The seepages at the head of Katalla Slough and on Redwood, Burls, 
and Chilkat creeks are all in the soft shales, which have previously 
been called the Katalla formation (/of section on p. 91). Those 
[between Redwood and Burls creeks are associated wth conglomer- 
ates of presumably higher position (e of the section). Such of the 
seepages of the Nichawak region as have been seen by the writer are in 
shales which closely resemble those referred to above. The Cape 
Yaktag seepages are said to be in Miocene sandstones and shales. 
RELATION TO THE STRUCTURE. 
The position of the seepages with reference to the structure is some- 
what vague and uncertain. Those west of Katalla are on steeply 
folded rocks in which the structural features have not been determined. 
The group on Redwood Creek and Katalla Slough is apparently in 
close proximity to a fault. The Burls Creek and Redwood Creek 
groups are each near the axis of an anticline, the Redwood Creek anti- 
cline being probably broken near or west of its axis by a fault. The 
seepages between Burls and Redwood creeks are on monoclinal con- 
glomerates. The general structure of the Nichawak region has not 
been determined, but the rocks have steep dips and are probably 
closely and complexly folded. The Yaktag region, which has not been 
visited by the writer, is said to have an anticline near and parallel to 
the coast, north of which the rocks have a monoclinal northward dip. 
The seepages are said to occur on the north flank of the anticline, par- 
allel to and not far from its axis. 
DESCRIPTION OF THE SEEPAGES. 
Petroleum seepages and gas springs are very numerous in many 
parts of the oil belt, and at some of them the flow of oil or of gas is 
large. 
Several large oil seepages were seen by the writer on the banks of 
Mirror Slough, near the mouth of Martin River. The petroleum 
comes to the surface from the clay and mud of the valley floor, and 
a large amount has accumulated in the pools on the swampy surface 
