142 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
1899 the same locality was visited and described in some detail by 
Mr. Alfred H. Brooks, a of the Geological Survey, while en route from 
Pyramid Harbor to Eagle City with Mr. W. J. Peters. In addition to 
the Kletsan Creek occurrences Mr. Brooks gives notes on the exten- 
sion of the copper belt toward the west. 
In 1900 Messrs. Schrader and Spencer b visited the southern field 
and issued a comprehensive report on its geology and mineral 
resources, particular attention being given to the copper occurrences. 
In 1902, while Mr. W. C. Mendenhall extended the earlier work of 
Messrs. Schrader and Spencer in the western portion of the southern 
field, Mr. F. C. Schrader visited the region about the head of the 
Copper, the Nabesna, and the Chisana rivers. The results of all these 
studies, with such information as can be gleaned from other sources 
concerning the localities which the geologists have not visited, will 
shortly be issued as a paper on the mineral resources of the Mount 
Wrangell district, and for a full account of what is at present known 
on the subject this report should be consulted. Only that portion of 
it which bears upon the copper occurrences is summarized here. 
SOUTHERN DISTRICT. 
This, the best known and probably the richest of the two copper 
belts of the region, occupies a strip nearly LOO miles long and of vary- 
ing width along the southern base of the Wrangell Mountains. 
Throughout this zone, in the drainage basins of the Chitina, the Kot- 
sina, ami the Cheshnina there are scattered deposits of copper ores, 
some of them very promising. 
GEOLOGY/ 
The lowest si rat igraphically, and therefore the oldest, of the econom- 
ically important formations of this belt, is a great series of successive 
basalt flows, now somewhat altered, which has been called the Nicolai 
greenstone. A thickness of not less than 4,000 feet of this basalt is 
exposed near the western part of the area in which it is known, and 
its maximum may be very much greater, as the base of the formation 
is nowhere exposed. The thin sheets in which this fluid lava issued 
now lend themselves to the determination of structure in the forma- 
tion almost as well as does bedding in sedimentary rocks. 
After the close of the period of great volcanic activity of which the 
Nicolai greenstone is the record an era of sedimentation set in, appar- 
ently without any intervening erosion. The first of the sediments 
deposited was a massive white limestone, which is particularly promi- 
nent along the Chitistone River and has therefore been called the 
«A reconnaissance from Pyramid Harbor to Eagle City, Alaska: Twenty-First Ann. Rept. 
U. S. Geol. Survey, Pt. II, 1900, p. 377 et seq. 
b Geology and mineral resources of a portion of the Copper River district, Alaska. Special 
publication of tbe U. S. Geol. Survey, 1901. 
cThis account of the geology is summarized from the report of Schrader and Spencer. 
