THE K AT MAI REGION, ALASKA 



573 



Russell, who says: "This belt of igneous activity is nearly i,6oo 



miles long It is so narrow and well defined that two 



parallel lines drawn on a map of Alaska, twenty-five miles apart, 

 may be made to include nearly every volcano in the belt that is 

 known to have been active in historic times."' 



It seems that such a linear distribution must indicate a major 

 fracture in the earth's crust, and we might expect to find plain 



Fig. 3. — View across canj^on of Katmai River, from lower slopes of Mount 

 Katmai, looking at Barrier Range. These mountains consist of shale and sandstone, 

 believed to be of Upper Jurassic age, in beds gently inclined away from the observer, 

 with some igneous intrusives. Photograph by D. B. Church, 1916. 



evidences of dislocation of strata or even profound disturbances 

 associated with it. On the contrary, very little evidence of this 

 kind is apparent in the region explored by us. On the northwest 

 side of the belt masses of Upper Jurassic sediments (Spurr's Naknek 

 series), 5,000 feet at least in thickness and possibly much more, lie 

 in horizontal, undisturbed strata, whose continuity may often be 



' I. C. Russell, Volcanoes of North America, p. 268. 



