256 A. II. BROOKS — RECONNAISSANCES IN SOUTHEASTERN ALASKA 



mainland coast. The otherwise smooth coastlines of the island are 

 broken by numerous fiords similar to those which penetrate deeply into 

 the adjacent Coast range. The islands are separated from each other 

 and the mainland by deep and often very narrow waterways. Some of 

 these, like Lynn canal, penetrate far inland. An examination of a map 

 will show that these features have a more or less parallel arrangement, 

 and attention will be drawn to the fact elsewhere that the direction of 

 these channels is consequent on structural lines in the bed rock. 



In southeastern Alaska four rivers of considerable size — the Alsek, 

 Chilkat, Taku, and Stikine — have their sources in the Interior Plateau 

 region, and reach the sea after traversing the coastal ranges. The Chil- 

 kat flows through the depression which separates the northern extension 

 of the Coast range and the Saint Elias mountains. There are many 

 minor streams on the mainland of southeastern Alaska which have their 

 sources within the Coast range. The drainage of the islands of the 

 Alexander archipelago is usually carried to the sea by small streams. 

 The lack of topographic maps makes it impossible to describe them in 

 any detail. 



Geology 

 stratigraphy 



While but few of the details of the geology of southeastern Alaska 

 are known, and even the general succession of beds is very much in 

 doubt, yet the distribution of certain lithologic types is fairly well estab- 

 lished. The general trend of the rocks is in a northwest and southeast 

 direction parallel to the coastline. There are certain lithologic types 

 occurring as belts running parallel to this strike, which seem to persist 

 with rather remarkable uniformity from Dixons entrance to Lynn canal 

 and Icy straits. 



The granite which forms the Coast range is the best defined of the 

 lithologic belts, and has been traced, practically without interruption, 

 from Portland canal to the head of Lynn canal. East of the granite 

 belt are a series of quartz-schists and limestones, which seem to be fairly 

 persistent from Bennett lake southward. These are in turn succeeded 

 to the eastward and unconformably overlain by younger sediments. 

 To the west of the granite is a belt of black phyllites and arenaceous 

 schists, which are locally much metamorphosed and include many 

 greenstone schists. These are fairly persistent throughout southeastern 

 Alaska. To the west of the phyllite belt bluish limestones have been 

 observed at a number of localities. This belt has not been so well 

 traced. Still farther west is a belt of white and blue crystalline lime- 

 stone associated "with phyllites. These rocks are very persistent, and 



