222 ALASKAN MINERAL RESOURCES IN 1906. 
thickness of these underlying deposits was not determined, bul or 
section was observed in which 100 feet of them was exposed. Tr. 
sands and clays of the intermediate member are naturally less col 
spicuous than the underlying beds, but have in many places becoJ 
indurated by the burning of the coal beds and baked to a conspicuor 
red color. The overlying gravels at the localities where their relatior 
to the underlying deposits were observed, whether in horizontal c 
tilted strata, were found to be structurally conformable. They ai 
characterized by a yellow color. They include both fine and coan 
material, are well worn and well rounded, and the predominant cor 
stituents are white quartz and chert of various colors, principal 
black. There is a considerable proportion of metamorphic rocks an 
many pebbles of compact chert conglomerate. In the upper part < 
the gravels, in strong contrast with their medium- to fine-graine 
material, are locally many bowlders of granitic rocks and diabase an 
a few well-rounded bowlders of dense chert and quartzite conglon 
erates. The greatest observed thickness of these deposits was approx 
mately 3,500 feet. The upper gravels constitute about half of th 
entire deposit. 
Fossil leaves are observable nearly everywhere in the beds assc 
ciated with the coal, but except where these beds have been baked b 
the burning of the coal the fossils are poorly preserved. The age ( 
the coal-bearing member has been determined as Kenai. The age ( 
the gravels has not been determined, nor is it definitely known tha 
they are chronologically conformable with the underlying deposit; 
but they have been folded at every point where folding was observe! 
along with the underlying deposits. Where valleys have been exte 
sively developed in these deposits bench gravels have in many plac 
been laid down on the truncated edges of the older deposits, and whe 
these older beds are horizontal the bench gravels are in apparent co 
formity with them, obscuring the relationship. It is probable tha 
deposits of various ages since the Kenai, formed under varied cond 
tions of sedimentation, occur in this area and that the coarse materh 
in the uppermost part of the gravels owes its origin to glaciation. 
Parts of the gravel members of these deposits are auriferous an 
have supplied the gold for the Bonnifield region. There is a marke 
resemblance between these coal-bearing deposits, with their thick bed 
of overlying gravels, and the 4 Kenai beds of the Seventymile Cree 
area near Eagle, with their coal-bearing deposits and thick beds c 
conglomerate formed largely of the same kinds of material. Thes 
latter beds also, as was observed by Brooks in the Woodchoppe 
Creek area during 1906, are auriferous. 
