W wrIght N1> ] DEVELOPMENTS IN SOUTHEASTEEN ALASKA. 
Among the islands of the archipelago a particular formation is not 
continuous along a definite line, and cross sections vary in different 
latitudes. These islands are composed in the main of wide, intrusive, 
granitic belts, often forming the core of the islands; of Paleozoic, lime- 
stone beds in places several miles in width, and of wide areas of intru- 
sive greenstones, usually schistose. On some of the islands black 
slates are prominent, and probably form the bed rock of many of the 
channels. Where slates occur in the vicinity of an intrusive belt they 
are invariably altered to mica-schist and hornfels, and similarly many 
of the limestone beds have been changed to marble. In the vicinity 
of Sitka and farther southward, along the Pacific coast, extensive 
though relatively narrow belts of gray wacke form the country rock. 
A very much younger group of comparatively flat-lying rocks rest 
upon the upturned and eroded edges of the older sediments. They 
comprise a series of sandstones and conglomerates interstratified with 
numerous coal seams containing fossils of Eocene age." These beds 
appear to have been deposited in relatively low, flat areas, notably on 
Admiralty and Kuiu islands, subsequent to the upheaval of the moun- 
tain ranges, and were not subjected to the dynamic forces which caused 
the metamorphism and folding of the underlying limestones and 
associated strata. These Eocene beds show evidence of only gentle 
folding accompanied by slight faulting. 
Subsequent to the deposition of the coal beds portions of the two 
above-mentioned islands were covered by flows of andesitic lava, dikes 
of which are also found on many of the other islands, cutting the older 
sediments. 
MINERALIZATION. 
Lode systems, following definite geologic horizons, have been traced 
for many miles along the west slope of the Coast Range. These lodes 
occur within limited zones of mineralization, which follow the trend 
of the sediments and form irregularly disposed concentrations of min- 
eral, sometimes sufficient to make an ore. Such zones were observed 
by A. C. Spencer and the writer along the mainland, from Berne is 
Bay to Windham Bay, and are described in a general way in the pre- 
liminary report on the Juneau gold belt. 5 What seems to be the 
southern continuation of these mainland belts traverses the Wrangell 
and Ketchikan districts. They are presumably represented by the 
mineral locations in Port Houghton, Thomas Bay, Glacier basin cast 
of Wrangell, Bradfield Canal, and Thorne Arm east of Ketchikan. 
The data collected from the mineral outcrops and mines of the many 
islands of this territory have not been sufficient to define the existence 
aDall, W. H., Coal and lignite of Alaska: Seventeenth Ann. Kept. U. S. Geol. Survey, pt. 1, pp. 
769-908. Brooks, A. H., The coal resources of Alaska: Twenty-second Ann. Kept. U. S. Geol. Survey, 
pt. 3, pp. 515-571. 
&Spencer, A. C, The Juneau gold belt, Alaska: Bull. U. S.Geol. Survey No. 225, pp. 28-42. 
Bull. 259—05 4 
