572 CLARENCE N. FENNER 



relief, and the higher summits are but little inferior in elevation 

 to those of the volcanic belt, but dissection has here reached a 

 stage at which broad valleys of moderate slope have been developed. 

 The line along which arise the active or recently active volcanoes 

 is one of the longest and most .clearly defined volcanic chains in 

 the world. At its northeast end the farthermost volcano whose 

 character is definitely known is Mount Redoubt, though Mount 

 Spurr, Black Peak, and Double Peak, from their position and charac- 

 teristics, appear to prolong the range still farther to the northeast. 

 These all lie well in the interior, among characteristically conti- 



FiG. 2. — The Katolinat Mountains, between foot of Valley of Ten Thousand 

 Smokes and head of Naknek Lakes. These mountains show sections of Upper 

 Jurassic shale and sandstone, several thousand feet in thickness, in horizontal strata. 

 Postglacial canyon in foreground. Photograph by J. D. Sayre, 1918. 



nental structural features. Thence the range runs southwestwardly 

 to the base of the Alaska peninsula, and follows the latter through- 

 out its length. Here its course lies through a region of nearly 

 horizontal sediments at only a moderate distance from the edge 

 of the continental shelf, but where, at about the end of the Alaska 

 peninsula, the edge of the shelf curves to the northward, the line 

 of volcanoes continues without deviation and strikes off across 

 oceanic deeps of 1,000 to 2,000 fathoms. The Aleutian Islands 

 and their volcanoes form the summits of a narrow, steep-sided 

 ridge, with great depths of water on both sides. The well-defined 

 character and continuity of this volcanic belt were noted by I. C. 



