MATANUSKA AND TALKEETNA BASINS. ^09 
steeply to the south. There is physiographic evidence of faulting at 
the base of this ridge, as well as of block faulting within the lower 
hills of the valley. A fault occurs near the base of the mountains on 
Eska Creek. Another may be observed on Chickaloon Creek, near 
the northern edge of the valley. The trend of these faults and their 
occurrence in rough linear arrangement along the northern boundary 
suggest structural rather than erosive origin of the Matanuska Valley. 
East of Hicks Creek the older rocks of Jurassic age do not present 
the same structural features. The sediments of the upper Jurassic 
trend northwestward, whereas those of the lower middle Jurassic 
strike in a northeasterly direction. Block faulting and open folding 
are present in both of these formations also. More data must be col- 
lected before the nature of the relations of the older rocks to those of 
Tertiary age can be clearly understood. 
ECOXOMIC GKOTLOGY. 
COAL. 
AREAL DISTRIBUTION. 
So far as known, the Tertiary coal-bearing rocks occurring in the 
Matanuska basin cover an area of about 380 square miles. Coal-bear- 
ing rocks of Mesozoic age developed in the upper Matanuska basin 
cover approximately 500 square miles. The areal extent of these 
divisions is shown on the map (fig. 2, p. 106) and the character of the 
beds has been described above. The mapping of the coal-bearing 
rocks must in no sense be taken to mean that areas so mapped are 
underlain by workable coal seams. So far as known, the actual area 
underlain by coal from Tsadaka Creek to Hicks Creek, inclusive, 
approximates 70 square miles. Localities where coal of commercial 
importance has been observed will be described. 
There are three kinds of coal within the region — anthracite coal, 
confined to a small area in the Mesozoic rocks; high-grade bitumi- 
nous coals, occurring in the eastern portion of the Tertiary field; and 
high-grade lignite, found in the western division of the Tertiary field 
and in certain localities in the upper Matanuska Valley associated 
with Mesozoic rocks. 
Coal outcrops have been observed on Tsadaka, Eska, Kings and its 
tributaries, Chickaloon, and Coal creeks; on the small streams head- 
ing in the Talkeetna Mountains between Boulder and Hicks creeks; 
on Hicks and Billy creeks; and on the banks of Matanuska River 
about 3 miles above the mouth of Chickaloon Creek. They have also 
been reported from Boulder and Caribou creeks, from a creek on the 
south side of the Matanuska 9 miles above Coal Creek, and from 
Little Susitna River. 
