MATANUSKA AND TALKEETNA BASINS. Ill 
and ill the other an aggregate thickness of 11 feet 6 inches of coal, 
though no seam exceeded 2 feet 6 inches in thickness. At the first 
locality the strike is N. 70° W. (magnetic) and the dip 40° S.; at the 
second the strike is N. 80° E. (magnetic) and the dip 34° S. 
In a small creek west of Purinton Creek is exposed a synclinal of 
coal, 3 feet thick, cut off by a heavy diabase dike, as shown in fig. 3. 
It is believed that the anthracite of this region covers only a small 
area. The rocks are closely folded, and the seams are cut off by thick 
diabase dikes. Though it is not certain that the intrusion of diabase 
dikes is the cause of the anthracitic nature of the coal in this vicinity, 
its presence at least suggests the possibility of such an influence. At 
other localities in areas of Tertiary rocks diabase dikes are found in 
immediate contact with bituminous coals, which in some places have 
been altered to a dense coke. None of these latter coals can be classed 
as anthracite. However, in the vicinity of the anthracite, diabase is 
present in greater mass than elsewhere observed near the coal, and 
it is reasonable to suppose that the heat derived from its presence 
was at least a supplemental agency in causing the formation of 
anthracite. 
BITUMINOUS. 
The bituminous coal held of the lower Matanuska Valley may be 
divided into two districts — the eastern and western. Under the first 
may be included the coals of Kings and Chickaloon creeks and those 
on both sides of the Matanuska in the vicinity of Chickaloon Creek; 
under the second, the coals of Tsadaka and Eska creeks. 
EASTERN DISTRICT. 
Martin " states in regard to the coal of the eastern district : 
The coal in this area all possesses about the same physical characteristics, and, as will 
be seen by the analyses, the variation in chemical composition is not great and sup- 
ports this grouping. It has the ordinary properties of most bituminous coal. It is soft 
and fragile, but often without any well-defined planes of fracture. It burns with a short 
flame and a small amount of smoke and possesses distinct caking properties. The 
seams generally contain a large amount of impurities, both in the form of thick partings 
of shale and as thin bands of shale and bone. Many of these can not be separated in 
mining. The coal is soft and friable, and much of it will not stand severe handling 
without crushing. Pyrite is present both as balls and as scales, but not abundant. 
The friable character of the coal is not a great detriment when it is considered that 
much of it will probably have to be crushed and washed (especially for coke making) 
and that the coal when used for steam or heating will cake as soon as put in the furnace, 
so that there will consequently be little or no loss through the grates. 
On the south bank of Matanuska River, 3 miles above the mouth 
of Chickaloon Creek, three coal seams have been found. The upper 
seam, 7 feet thick, is separated from the middle seam by 43 feet of 
shale and a 6-inch stringer of coal. The lowest seam, 5 feet 8 inches 
thick, is separated from the middle seam by 13 feet of shale, which 
a Op. cit., p. 19. 
