104 ALASKAN MINERAL RESOURCES IN 1905. 
UPPER JURASSIC. 
The upper Jurassic sediments, best developed on the shores of Herendeen Bay soutl 
of Coal Creek, outcrop in massive bluffs, where weathering has caused the formation of 
large spherical masses weighing, in some instances, several tons. Long cylindrical shapes 
are common, and conchoidal fsacture characterizes the formation. 
Doctor Stanton says of the fossils collected in these rocks: 
Three small lots from the "bluff south of Moss Valley" contain Aucella of another type, resembling 
Aucella pallasi Keyserling, which is a Jurassic form. With this species are also specimens of Plevr 
romya and Belemnites. These lots are believed to be from the .Jurassic. 
Tlie single specimen from "blufl south of Lawrence Creek" shows only the imprint of a. fragment 
of an ammonite too imperfect for even generic determination. 
It will be seen from the above that in the immediate vicinity of the coal there arc found 
throe distinct horizons— viz, Oligocene, Upper Cretaceous, and Lower Cretaceous — and that 
in the neighborhood of Herendeen Bay there are in all four horizons, as the upper Jurassic 
was found on the shore of the bay in a ''bluff south of Moss Valley." 
The coal-bearing beds of Upper Cretaceous age may be correlated with the Upper Cre- 
taceous beds of Chignik Bay and the Upper Cretaceous coal-bearing strata of VancouvJ 
[sland. The coal beds near Nulato, on Yukon River, are also of Upper Cretaceous age. 
Nearly due east from the Herendeen Bay field, in an air line approximately 14 miles 
distant, \V. H. Dall collected on the shores of Port Moller fossils of Mesozoic age (Lower 
Cretaceous) — Belemnites, Cyprina, and Aucella — determined by C. A. White in 1884. « 
Nearly south of this locality, on the southern side of the peninsula, at Stepovak Bay, 
Charles Palache collected invertebrate fossils of Eocene age,'' determined and deserihed 
by W. H. Dall/ while on the north end of Unga Island, of the Shumagin group, both Kenai 
and Miocene beds are exposed. (/ Therefore in an area approximately 40 miles square art! 
found strata ranging from upper Jurassic to .Miocene. 
[GNEOUS ROCKS. 
Though in the neighborhood of the coal no rocks of an igneous character were observed, 
an area of considerable extent to the south, on the trail between Herendeen and Portage 
bays, is characterized by volcanic rocks. The high ridge forming the north side of the 
valley of Portage Creek, approximately H miles from Herendeen Bay, is composed of a 
dark basic crystalline rock found to be a quartz-diabase. This rock and a second type, 
provisionally called a monzonitic porphyry, were found at several isolated points along the 
trail. The exact relation they bear to each other or to the underlying sandstone series 
is not known. 
Rocks of intrusive origin, resembling more or less the above types, were noted by Charles 
Palache' at Chichagof Cove, Stepovak Bay. 
STRUCTURE. 
Only the main structural features were determined, special attention being given to the 
position, condition, and possible continuance of the coal seams. 
The coal-bearing strata of Upper Cretaceous age, including both sandstones and con- 
glomerates, strike in a direction slightly north of east and dip rather steeply ('M)° 55°) to 
the north. Local variations are not uncommon, strikes varying from N. 65° E. to N. 80° E. 
(See fig. 6.) 
The rocks of Lower Cretaceous age (not coal bearing), forming the left side of the valley of 
Coal Creek, strike in a southeast-northwest direction and dip to the northeast at angles of 
aBull. U. S. Geol. Survey No. 4, 1884, pp. 10-15. 
b Harriman Alaska Expedition, vol. 4, New York, 1904, pp. 69-88. 
cldem, pp. 99-124. 
^Correlation papers— Neocene: Bull. U. S. Geol. Survey No. 84, 1892, pp. 240-242. See also Dall, 
W. H., Report on coal and lignite of Alaska: Seventeenth Ann. Kept. l. s. Geol. Survey, |>t. I. 1*96, 
pp.807 811. 
' ecology about Chichagof Cove, Stepovak Bay: Harriman Alaska Expedition, vol. I. New York, 
1904, pp. 69-88. * 
