312 Scientific Intelligence. 



tides. This points to a two-fold origin of the gold, as derived in 

 part from the rocks immediately about and in part from distant 

 and older rocks, which may have been worn down, possibly along 

 an old seashore, into terrace gravels, and then by subsequent 

 erosion brought into the present stream beds. Further explora- 

 tion in the hills to the south may disclose the true source of these 

 pebbles and of the gold that accompanies them. On American 

 Creek, in the Mission Creek district, the gold-bearing placers are 

 also derived from rocks of the Rampart series — quartzitic schists, 

 serpentines, and chloritic rocks — and the gold is said by Spurr to 

 have been derived mainly from the schistose zones in the bed- 

 rock. 



The richest gravels have been found in the Birch Creek and 

 Fortymile districts. In the entire Birch Creek district, which lies 

 south of Circle City, and on Miller, Glacier, Poker, and Davis 

 creeks of the Fortymile district, near the international boundary, 

 the bed-rocks are always the quartzite-schists of the Birch Creek 

 series, containing veins of quartz. The gravels rest, as a rule, 

 directly on the schist, though in some cases, as on Harrison and 

 Eagle creeks in the Birch Creek district, there is clay beneath 

 the gravels, and the gold as a rule does not extend into the bed- 

 rock but occurs chiefly at the top of the clay. Generally, how- 

 ever, the schist is rotted and reddened from oxidation for a few 

 inches to several feet below the surface, and in this part the gold 

 has settled into the cracks and joints. The pay gravels lie mostly 

 next the bed-rock, in an average thickness of perhaps 2 feet, 

 though sometimes up to 10 feet, while the overljing gravels 

 average 8 or 10 feet, with a maximum of 25 feet. In the gravels 

 the schist is in quite large, flat fragments, and the quartz is in 

 bowlders of varying size. The schist fragments lie flat, and are 

 mixed with sand, showing that the sorting action of running 

 water has not been carried far. In the concentrates from the 

 sluice boxes the heavier minerals associated with the gold — 

 galena, magnetite, limonite, hornblende, and garnet — are in each 

 case such as are found in the neighboring schists, and the nug- 

 gets of gold often have pieces of quartz still adhering to them. 

 All these facts are evidence that the gold is derived from rocks 

 in the vicinity, and is not brought from a great distance, perhaps 

 by glaciers, as some erroneously suppose. 



The rocks of the Fortymile series in the Fortymile district, as 

 already stated, form the west bank of Fortymile Creek, and 

 south of the South Fork cross the divide between Franklin Gulch 

 and Napoleon Creek, where they are overlain by green slates of 

 the Rampart series, which in turn are overlain by conglomerates 

 of the Mission Creek series. In Franklin Creek the bed-rocks are 

 marbles interbedded with mica- and hornblende-schists; the 

 gravel contains fragments of marble, quartzite, mica-schists, and 

 vein quartz. At one point a quartz vein is found in the bed-rock, 

 and below it native silver has been found in the gravels, which 

 apparently came from this vein. It is the schistose rocks that 



