122 ALASKA GLACIERS 



greater part of the inside passage, and our examinations 

 about Sitka occupied several days. An excursion to 

 White Pass gave a view of a canyon at the head of a 

 fiord, and of uplands at 2,000 to 2,500 feet altitude, but 

 the higher summits were seen only from stations at or 

 near sea-level. 



Direct observation of the uplands was afterward supple- 

 mented by the study of photographs. The U. S. Coast 

 and Geodetic Survey and the Canadian International 

 Boundary Commission have used the camera freely in con- 

 nection with topographic surveying, and I was so fortu- 

 nate as to have access to their series of pictures. The latter 

 organization spread a web.of triangulation over all the 

 mainland portion of southeastern Alaska, and from each 

 of the mountain peaks occupied as stations photographed 

 the entire horizon, using the views afterward for the con- 

 struction of contour maps. Their album thus represents 

 the upland in a systematic and thorough way and is emi- 

 nently adapted to physiographic study. (See page 6.) 



In this, as in other districts of Pleistocene glaciation, it 

 is evident that the Pleistocene sculpture is superposed on 

 an earlier sculpture, chiefly aqueous; and in the discus- 

 sion of the work of Pleistocene glaciers it is necessary to 

 consider the pre-Pleistocene condition. I find it conve- 

 nient to begin with that consideration. 



Pre-Pleistocene Topography 



So far as we saw the indurated rocks, and so far as we 

 know them from the descriptions of others, they are either 

 igneous or metamorphic. The igneous rocks are almost 

 wholly intrusive. The metamorphic exhibit various de- 

 grees of alteration, but all are so folded or squeezed that 

 the planes of structure make large angles with the hori- 

 zon. The general strike is believed to be parallel to the 

 coast, but there are few direct observations of strike. In- 



