on 
MATANUSKA AND TALKEETNA BASINS. 107 
2. Mica schists.— A narrow belt of these rocks borders the granites 
their southern side. On account of their strongly foliated and 
thoroughly metamorphosed character they are regarded as repre- 
senting the oldest rocks of the region. They possess considerable 
economic interest from the fact that locally they yield gold-bearing 
gravels, in places rich enough to be of commercial value. 
3. Slates and graywacke slates. — These rocks occupy an area near 
the mouth of Talkeetna River and probably extend up Susitna 
River. They are known to be more or less gold bearing and have 
yielded some creek and bar diggings. On account of the lack of 
fossil evidence the age of these rocks is not known. They show 
some similarity to the series to be described next. 
4. Graywacke-slate series, including some greenstones. — These rocks 
occur on the south side of Knik Arm, and are found striking into 
the Chugach Mountains on the south side of Matanuska River. 
They are a continuation of the rocks exposed in the Sunrise district 
on Turnagain Arm. No fossils have yet been found in them, so 
that their age is in doubt. They strongly resemble the rocks of 
Prince William Sound and are regarded by Mendenhall and Moffit 
as of probable upper Paleozoic age. The slates and graywackes are 
partially schistose and have been closely folded, uniformly present- 
ing isoclinal dips. They are cut by a great multitude of small 
quartz stringers, and it is possible that these rocks may yet be 
found the source of gold placers. 
5. Jurassic. — All the rocks of Jurassic age have been grouped 
together on the map. With them is included the lower Cretaceous 
limestone, whose distribution is limited to the headwater region of 
Matanuska and Nelchina rivers. These beds contain thin seams of 
low-grade bituminous coal. This is in marked contrast to certain 
localities in the Tertiary (Kenai) rocks, where strong seams of high- 
grade bituminous coal occur, a reversal of the usual state of affairs, 
in which the older rocks ordinarily carry coal of a higher grade than 
the younger rocks. In general the Jurassic rocks show only folding 
of an open character, but minor faulting is of widespread occurrence. 
6. Upper Eocene (Kenai). — Strata of this age comprise a series of 
sandstones, shales, and conglomerates, carrying workable seams of 
bituminous coal, chiefly developed within the lower Matanuska Val- 
ley. These beds represent a period of fresh-water sedimentation of 
upper Eocene age, as shown by the fossil plants contained in them. 
The rocks are well indurated, and, as first noted by Mendenhall, 
resemble the Paleozoic coal measures of the Appalachian region. 
Since they were laid down they have been subjected to sharp folding 
and now stand in vertical attitude in portions of the area. They 
are affected by a great number of faults of small throw. 
