206 ALASKAN MINERAL RESOURCES IN 1906. 
few miles after leaving the hills, meander sluggishly in no well- 
defined valleys and enter the Tanana with sloughlike inconspicuity 
The surface is sparsely timbered with small spruce, tamarack, birch, 
and aspen, with a larger growth near the major streams and along the 
base of the foothills. Swampy areas necked with lakes are inter- 
spersed with patches of birch where the ground is bare and dry, and 
the traveling therefore fairly good. Feed is good along the water- 
courses but during the long hot days of summer there is scant relief 
for the pack animals from the horseflies and mosquitoes, which render 
an otherwise friendly area a place of almost constant torment. 
The bed rock of the Bonnifield and Kantishna regions includes 
highly metamorphosed ancient rocks and loosely consolidated deposits 
of comparatively recent origin. The most common distinction made by 
the miners is that between hard and soft bed rock, and this distinction 
is warranted by the conditions. The ridges are formed for the most 
part of metamorphic schists and igneous rocks; the intervening lon- 
gitudinal valleys, of deposits in the main unconsolidated but older than 
those of the present streams. The most important fact from an eco- 
nomic view point is the distinction between the two groups of hard 
and soft bed rock. The hard bed rock from south to north includes 
a belt of highly metamorphosed schists, predominantly quart zitic 
schists with a small amount of interbedded crystalline limestone, and 
some carbonaceous schists; a belt of black slates with quartzite and 
cherty beds; and a belt of metamorphosed porphyritic feldspathic 
rocks. The belt of quartzite schists forms most of the bed rock in the 
Kantishna region, crosses Cantwell River just south of Healy Creek 
and extends northeastward to the south of the Bonnifield region; the 
slates occur in the high ridges at the head of the Totatlanika and the 
porphyritic feldspathic schists form the several ridges to the north 
These porphyritic schists occupy large areas in the northern foothills 
of the Alaska Range. They were observed throughout the area be- 
tween Cantwell and Wood rivers. To the south they are interrelatee 
with the black slates containing quartzite beds that succeed the quart- 
zite schists. To the north they form the outermost ridges overlooking 
the Tanana Flats. Throughout this area are several prominent east 
west ridges of these rocks rising 1,500 to 2,000 feet above the valley: 
that separate them. The color ranges from dark-gray to white. Th< 
prevailing tone is whitish, from the weathering of the large amount o 
feldspar that the rock contains, and much kaolinic material has beei 
contributed by this rock to the deposits that occupy large areas in th< 
longitudinal valleys between the ridges. The rock ranges in characte 
from a coarsely porphyritic sericitic variety with feldspars 4 dm. o 
more in diameter to a fine, evenly grained white or gray sericite schis 
with no grains visible to the eye. These rocks are of igneous origh 
