ALASKA AND ITS MINERAL RESOURCES 161 



along the Yukon river for 30 or 40 miles above the Yukon flats, 

 rocks with the characteristic dark coloring of the Rampart series 

 are exposed. From these up to the mouth of Mission creek rocks 

 of the Tahkandit, Mission creek, and Kenai series occupy the 

 banks of the river. On Mission creek itself only these later for- 

 mations are found, but the gold in the gravels is supposed to come 

 from the conglomerates (" cement rock 1 ') of the Mission creek 

 series, which contain pebbles of the older rocks. On American 

 creek, the main branch of Mission creek which comes in from the 

 south, the dark rocks, shales, limestones, and tuffaceous beds 

 which form the bed-rock are supposed to belong to the Rampart 

 series, which also occur along the Yukon river from five to ten 

 miles above Mission creek to within 25 miles of the mouth of 

 Fortymile creek. Above this to some distance above Fortymile 

 creek the river runs in beds of the Mission creek series. 



It is in the Fortymile district and the adjoining mining district, 

 on tributaries of Sixtymile creek, that the relations of the different 

 gold-bearing series are best seen. Here there is an east-west axis 

 or backbone running parallel to the upper part of Fortymile 

 creek and along the divide between it and Sixtymile creek, with 

 quartzite schists of the Birch creek series resting immediately on 

 it, both to the north and to the south. Above these, on either 

 side, are the marbles and alternating schists of the Fortymile 

 series. Fortymile creek below the forks runs for a considerable 

 part of its course along the junction between these two series, on 

 the northern flank of the anticline. Dikes of various eruptive 

 rocks, including intrusive granite, are very abundant, especially 

 on the South fork. On the upper part of this fork are green tuffs 

 and slates of the Rampart series, overlain unconformably by con- 

 glomerates, sandstones, and coaly shales of the Mission creek 

 series. Both the South fork and Sixtymile creek are supposed 

 to head in a backbone of granite around Sixtymile butte, which 

 is surrounded by quartzite schists of the Birch creek series. 

 These regions lie partly in American, partly in Canadian territory. 



The Canadian area has not been studied by American geol- 

 ogists, except in wayside observation along such routes of travel 

 as necessarily lay through it. The Canadian geologists, on the 

 other hand, did not in their earlier and published observations 

 recognize any subdivisions in the older rocks such as have been 

 made by Spurr. Hence it is not possible to attempt even a prox- 

 imate outline of the Canadian gold-bearing rock formations. 

 General geological data and local discoveries of gold-bearing 



