Wright.] TOPOGRAPHY AND GEOLOGY. 15 
Chilkat Lake, at the mouth of Salmon River, and two other lakes 
which fill basins at elevations of 1,200 and 800 feet in the hills just east 
of Porcupine, are probably the result of damming, either by glacial 
moraines or by alluvial gravels. 
The accompanying map (PL II), giving the main watercourses and 
their tributaries, is taken for the most part from the unpublished map 
made by the Boundary Survey Commission in 1892, though a few nec- 
essary corrections have been made as accurately as possible from foot 
traverses and topographic sketches. 
GEOLOGY. 
INTRODUCTION. 
The geologic reconnaissance of southeastern Alaska has led to the 
recognition of certain fairly well-defined belts of rocks extending 
parallel to the coast line, which have a striking lithologic uniformity 
along the extension of their strike. The great igneous complex which 
forms the country rock of the Coast Range is the best defined of these 
belts, stretching from British Columbia throughout southeastern 
Alaska. While the dominating rock of this mass is of a granitic 
appearance, and was so designated by Dawson 6 and others, microscopic 
studies have shown it to be more closely related to dioritic rocks. 
West of this Coast Range igneous belt are found metamorphic rocks 
of various types which will probably eventually be differentiated into 
a number of formations. The age of these metamorphic terranes is 
not definitely determined, but probably falls largely in the Paleozoic. 
The area under discussion contains both sedimentary beds, usually 
considerably metamorphosed and probably falling into the above- 
described zone of altered elastics, and igneous intrusives of the Coast 
Range zone. 
The general distribution of the sedimentary and intrusive rocks of 
this region is shown on the accompanying geologic map (PL V). The 
Porcupine district lies a few miles southwest of the Coast Range dio- 
ritic belt, which is here about 80 miles across. Adjacent to this on the 
south is a zone, 8 miles wide, occupied principally by metamorphic 
black slates, phyllites, and limestones, with strongly developed cleav- 
age parallel to the general northwest-southeast trend of the diorite 
contact, this being also the general direction of Klehini Valle} T . This 
sedimentaiy series is limited on the south by an outlying band of dio- 
rite from 2 to 4 miles in width, also striking northwest and southeast. 
This diorite band narrows toward the southeast, extending in this direc- 
a Brooks, Alfred H., Preliminary report on the Ketchikan mining district, Alaska: Prof. Paper U.S. 
Geol. Survey No. 1, 1902. Spencer, Arthur C, The Juneau gold belt: Bull. U. S. Geol. Survey No. 225, 
1904, pp. 28-43. 
b Dawson, G. M., Report on an exploration in the Yukon district and northern British Columbia: 
Ninth Ann. Kept. Geol. Survey Canada, vol. 3, pt. 1, 1888, p. 128. 
