THE MINING INDUSTRY IN 1906. 23 
they contain over 99 per cent of all the gold mines in the Territory. It 
does not follow, however, that there are no precious metals outside of 
the metamorphic areas. For example, the Apollo mine on Unga 
Island, in southwestern Alaska, is in a series of comparatively recent 
lava flows which have been altered only very locally. Again, some of 
'the Tertiary conglomerates in the Yukon basin are known to be aurif- 
erous, but it should be said that in this case the gold was undoubtedly 
derived from the metamorphic terranes. These exceptions to the 
general law are of importance because they show that other forma- 
tions than those indicated as metamorphic may contain precious 
metals. 
The map clearly shows that there are three general zones of meta- 
morphic rocks in Alaska. One skirts the Pacific seaboard, stretches 
through southeastern Alaska, and appears to occur again on lower Cop- 
per River, on Kenai Peninsula, and on Kodiak Island. It is not to be 
inferred that this belt is made up entirely of formations of the same 
age, though such may prove to be the case. The map is intended 
simply to express the fact that in this belt there are considerable areas 
of metamorphic rocks. In southeastern Alaska these altered rocks 
belong to Paleozoic terranes, but to the west no definite age determi- 
nation has been made. 
A second and much larger belt of metamorphic rock lies to the 
north and west of the coastal zone, stretching from the international 
boundary through the Yukon and Tanana region, and appears to 
trend to the southwest, paralleling like the first the larger structural 
features of the Territory. This belt is broken near Yukon River by 
younger beds, but appears again in Seward Peninsula. A third belt, 
whose relation to the second has not been established, as the inter- 
vening areas are occupied by younger sediments, stretches through 
the upper Koyukuk Valley and is found again on the Kobuk. 
Though the map suggests that the easterly extension of this third 
zone should be found in the Porcupine Valley, yet the work of E. M. 
Kindle has shown that while the same rocks are probably present near 
the point where the international boundary crosses the Porcupine, 
they are there not altered. This emphasizes the well-known fact that 
although a group of terranes may be highly altered in one locality, its 
extension may be made up of slightly altered rocks. The prospector 
should bear this fact in mind in seeking for new mining fields. So far 
as the evidence goes, the Porcupine basin does not seem a promising 
field for gold discoveries. On the other hand, the metamorphic rocks 
of Seward Peninsula probably find an extension east of the locality 
where they are indicated on the map. The metamorphic rocks of the 
inland zones are probably chiefly of Paleozoic age. Between the two 
general zones of metamorphic terranes there are some smaller belts of 
