62 ALASKAN MINERAL RESOURCES IN 1905. 
CRYSTALLINE ROCKS. 
The crystalline rocks, which are evidently the oldest, consist of a great variety of both 
igneous and metamorphic types. It includes granite and other plutonic igneous rocks, 
different kinds of gneisses and schists, slates, and stretched conglomerates. The crystalline 
rocks lie farther inland than the Yakutat series,^ and the boundary between the two is a 
nearly straight line extending along the northwest arm of Russell Fiord, crossing Nunatak 
Fiord diagonally, and thence running across the mountains to Hidden Glacier, which occu- 
pies the next large valley south of Nunatak Fiord. Where the two series outcrop on the 
south shore of Nunatak Fiord and in the Hidden Glacier valley they are evidently sepa- 
rated by a fault; and an extension of this fault would carry it down the northwest arm of 
Russell Fiord. In consequence of this difference in formation, the northeastern shore of the 
northwest arm of Russell Fiord is bordered by slate and the southwestern shore by the 
Yakutat series. No fossils were found in the crystalline rocks to indicate their age, but the 
great amount of intrusive 1 rock and the highly metamorphosed nature of the sedimentaries 
indicates a greater age than that of the neighboring Yakutat scries. 
YAKUTAT SERIES. 
Between the crystallines and the foreland, both on the peninsula and in the mountains to 
the northwest and southeast of it, there is a complexly folded and faulted series of rocks in 
which th< three most prominent elements are (1) a series of thinly bedded black shales and 
gray sandstones, (2) a black-shale conglomerate, with crystalline pebbles and bowlders, and 
(3) a massive crystalline rock of peculiar nature and relations. In some places this last rock 
is sandy in character and in others conglomeratic, including angular fragments of black 
shale in bands. Under the microscope it appears to be fragmental and shows quartz, fresh 
feldspar, mica, and other minerals. For the present, awaiting further petrographic study, 
this rock is tentatively classed as an indurated tuff. It occurs in great masses and is the 
most prominent rock in the Yakutat series. 
In addition to these rocks there are lesser areas of coarse conglomerates, occasional dikes, 
and limited areas of granite, crystalline limestone, and a dioritic rock. The field relation of 
the granite and other crystalline rocks indicates that these are the basement on which the 
true Yakutat series rests, with the black-shale conglomerate at the base of this series. 
It was found impossible to work out the succession in the Yakutat series, or to make even 
an approximate estimate of its thickness. The entire series is complexly folded in great 
compressed, overturned folds and is complicated by an intricate series of minor folds, con- 
tortions, and faults. The folding and faulting has often resulted in a veritable kneading of 
the rock strata, and frequently in a brecciation. A score of faults are often visible on a 
single outcrop a few square yards in area. But this complex folding and faulting has not 
sufficed to metamorphose the strata. 
The Yakutat series is remarkably unfossilifcrous, not because of destruction of the fossils, 
but evidently because of their original absence from the beds. Plant fragments and some 
animal remains occur occasionally in the thin bedded shale-sandstone strata, but a careful 
search failed to discover any beds yielding abundant or characteristic fossils. The report of 
T. AY. Stanton indicates that the fossils are not sufficiently typical to determine the age of 
the series. 
COAL-BEARING BEDS. 
Just outside of the mountain front, on the west side of the head of Yakutat Bay, occurs 
what is apparently a younger series than the Yakutat It consists of sandstones, clays, 
brown shales, and some coal beds. These beds dip steeply westward (45°-75°) and are 
a The terms Yakutat, Rampart (p. 130) . Orca (p. 80), and Valdez (p. 80) series were applied by the early 
explorers to large heterogeneous aggregations of rocks about which little was known The names are 
still retained although tins use of the word' series" is not in accord with the rules ol nomenclature 
given in the Twenty-fourth Annual Report. With more detailed work, these aggregates probably 
will be subdivided, and the word "series " abandoned. 
