ALASKA. 47 
was called to a mineral found associated with the gold in the sluice 
boxes, which proved to be cassiterite — the oxide of tin. The source 
of this mineral was not definitely ascertained, but it was found in 
streams draining areas of slates which contained quartz and calcite 
seams and were penetrated by intrusives of diabasic character. The 
publication of a timely report by the Geological Survey stimulated 
interest among prospectors, which led to further knowledge of the 
distribution. In the following season work was continued by the 
Survey, and it was suggested that a source might be found in the 
vicinity of the granite contacts. One of the most interesting devel- 
opments of the year 1903 was the tracing of the tin ore to deposits in 
granitic dikes, and this was accomplished mostly through the work of 
the Survey party. In other localities it seemed to have been derived 
from the slates. The investigation of this occurrence, in reference to 
the distribution and association of the stream tin, the location of the 
lode deposit, and the geologic maps, indicating similar rock occurrences 
where tin might possibly be found, constitute illustrations of the 
value of the Survey work to the people of Alaska. 
In 1895 the localities along the southern coast where coal exists in 
quantities of economic importance were visited and the character of 
the coals was determined. In connection with this work a large amount 
of material was assembled relating to coals and their analyses and to 
the distribution of the coal-bearing rocks throughout Alaska. 
In addition to the regular work of the Survey, reports are occasion- 
ally prepared that embody the results of several workers and place in 
compact form material which possesses much practical value. Such a 
report was published in 1901 on "The Coal Resources of Alaska." 
This includes a summary of the knowledge of the Alaskan coals up to 
the time of its publication. 
In connection with the work from the Kojoikuk to the Arctic Ocean^ 
the coals along the Colville River and at Cape Lisburne were found to 
occur in rocks of Mesozoic age; and as the rocks of the Colville area 
strike off toward Cape Lisburne, it is possible that the occurrences in 
the two areas are closely related. 
In 1902 the coal deposits of the Yukon were investigated and found 
to occur, with possibly one exception, in the upper Cretaceous and 
Kenai formations. The coals were grouped into those of the Circle 
province, the Rampart province, and the Nulato province. They range 
in character from high-grade lignites to semibituminous coals. 
In 1903 a party was sent to the region in the vicinity of Controller 
Bay to investigate the occurrence of oil. The coast from the vicinity 
of the Copper River delta to Cape St. Elias was visited, also a large 
portion of the valley of the Chilkat River. Later the oil fields on the 
west coast of Cook Inlet and of Cold Bay, on the Alaska Peninsuln, 
were investigated. 
