MATANUSKA COAL FIELD. 89 
lays from Seattle (<» Seldovia and one or two days by local steamers on Cook Met. There 
s a good horse (rail from Knik to the coal field. It requires a, day or a day and a half to 
p from Knik to Tsadaka Creek, and a day from Tsadaka Creek to Chickaloon Creek. Sup- 
dies can he purchased at Knik, where there are two stores, and natives can usually be 
secured there. Horses can sometimes he hired at Knik, hut it is not safe to depend on them 
mless arranged for in advance. 
OUTLINE OF THE GEOLOGY. 
The rocks in that part of the Matanuska Valley which was visited by the writer consist of 
loal-bearing sediments, partly Mesozoic and partly Tertiary, two distinct horizons appar- 
sntly being represented; Jurassic rocks, known only from stream bowlders; a large number 
end considerable variety of dikes and volcanic flows, granites and other coarse crystalline 
ocks bordering the valley on either side; and a large amount and broad extent of very young 
;ravels. 
COARSE CRYSTALLINE ROCKS. 
These rocks occur in the high mountains on either side of the Matanuska, Valley. They 
,re known to the writer only from the stream bowlders, from the reports of prospectors, and 
rom the appearance of the mountains as seen from a distance. They appear to consist 
hiefly of granite and diorite, although a variety of other rocks, including greenstone, is 
►resent. 
MESOZOIC ROCKS. 
Bowlders of dark, hard sandstone of very different lithologic character from anything 
een in place by the writer were found in the bed of Chickaloon Creek. They contain many 
pecimens of Aucella of an upper Jurassic species. The presence of upper Jurassic rocks in 
he Talkeetna Mountains is thus established. The bowlders were much worn and not abun- 
lant, indicating that the outcrops of these beds are at a considerable distance from the 
latanuska. 
A sharp ridge, about 5,500 feet high, borders the north side of the Matanuska Valley 
•etween Boulder and 1 licks creeks. It is part of the southern front of the Talkeetna Moun- 
ains. This ridge consists chiefly of gray wacke, with numerous calcareous concretions and 
>eds of anthracite coal. About midway on this ridge a Aery few fragmentary fossils were 
'btained, which indicate an age between middle Jurassic and upper Cretaceous. 
Kocks of possibly the same age were seen by Mendenhall" near the headwaters of Bubb 
,nd Caribou creeks, about 25 miles northeast of the locality just mentioned. 
TERTIARY ROCKS 
The rocks in the valley of the Matanuska from Chickaloon Creek to Tsadaka Creek con- 
ist chiefly of shale and sandstone, with many coal and lignite beds and at least one bed of 
aassive conglomerate. The conglomerate belongs near the top of these rocks, which alto- 
ether can not be less than 3,000 or 4,000 feet thick. 
There is [little doubt that part, at least, of these beds are of the same age as the coal- 
bearing rocks at Homer, on Cook Inlet, which are generally considered to belong to the 
jiddle Tertiary (Oligocene). 
GRAVELS. 
The valley of the Matanuska and its tributaries from the head of Cook Inlet to a point 
omewhat above Chickaloon. Creek is covered with thick deposits of coarse gravels which 
ccur in a series of benches or terraces, often concealing all of the hard rocks. The gra\ els 
re composed of bowlders of diverse character and vary in size from line sandstone to mate- 
ial a foot or more in diameter. It is reported that they carry very small amounts of gold, 
ut, so far as is now known, not enough to be of value even where the gravels have been 
Bworked by the streams that are cutting through them. 
a Mendenhall, W. C, A reconnaissance from Resurrection Hay to the. Tanana River, Alaska, in L898: 
'wentieth Ann Rept. U. S. Geol. Survey, pt. 7, 1000, pp. 265-340. 
