48 ALASKAN MINERAL RESOURCES IN 1906. 
BEDDED ROCKS. 
Limestone, slate, sandstone, and conglomerate, with intercalated 
greenstone and tuff beds, constitute the stratified rocks. In most 
places these have been profoundly met amorphosed and are represented 
by the crystalline limestones, mica and chlorite schists, cherts, and 
graywackes. 
By far the greater portion of the rock strata are of Paleozoic age. 
These consist of the metamorphic limestones, schists, cherts, green- 
stones, and other rock types, which together form the underlying 
bedded rocks of the entire area. The Mesozoic and Tertiary forma- 
tions are represented by the unmetamorphosed conglomerate, sand- 
stone, and shale beds, which in places are coal bearing. They are only 
local in occurrence and of no great extent, occupying limited areas on 
Admiralty, Kupreanof, Kuiu. and Prince of Wales islands. Basaltic 
lava flows of late Tertiary age cover the southern portion of Admiralty 
Island, the northeast side of Kuiu island, the south shore of Kupre- 
anof Island, and a small area on the south end of Prince of Wales 
Island. Overlying these rock strata are beds of clay and gravel and 
the recent volcanics at Mount Edgecumbe and at points along the 
mainland. 
INTRUSIVE ROCKS. 
The intrusive rocks occupy aboul one-half of the aggregate land 
area of southeastern Alaska, as is well shown on the accompanying 
map (PL III). Coarse granular rocks, granitic in character, form 
the great mass of the Coast Range 1 bordering the mainland and occupy 
wide areas in the central portion of many of the islands. They are 
in direct relation to the geologic structure, and their longitudinal 
axes and lines of contact parallel the direction of strike of the bedded 
rocks. Such Lntrusives vary in composition from granodiorite to 
quartz diorite and hornblende diorite. In general they invade the 
Paleozoic bedded rocks, but do not cut the more recent Mesozoic 
beds. Other intrusives are those of andesite, diabase, basalt, and 
melaphyr, usually in the form of dikes cutting both the older and 
younger sedimentary rocks. 
STRUCTURE. 
The sedimentary formations distributed along the mainland strip 
and adjacent islands all strike northwest and dip, as a rule, steeply 
to the northeast. The structure of the outer islands includes two 
separate systems of large and small folds. The main system, which 
is the younger of the two, has a northwesterly axial trend and is most 
pronounced adjacent to the wide areas of the intrusive rocks- 
namely, along the mainland and on Chichagof and Baranof islands. 
The minor system, which in most places has been obliterated by the 
