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 developments 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 occasionally 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 Koyukuk 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 Peninsula, were investigated.