GEOLOGIC MAP AND SECTIONS. 51 



hundred and fifty-fifth degrees of longitude. As the line of traverse 

 extends in a north-south direction across the trend of the terranes, 

 which has been found to be relatively constant, especially in the moun- 

 tains, the boundaries delimiting the various formations on the north and 

 on the south, along the line of the section, are approximately correct 

 and in some instances are well defined. In an east- west direction some 

 liberties have been taken in making such broad generalizations as 

 seemed permissible from the regularity of the terranes in the mountains 

 and their relations and lithologic resemblance to those previously 

 mapped to the east. 



The boundaries of the post-Paleozoic formations of the Arctic 

 slope, approximately determined on paleontologic and lithologic 

 evidence along the route of traverse, have been extended eastward 

 and westward on topographic evidence and on observations and 

 collections made by the writer in returning southward along the 

 coast from Point Barrow to Cape Lisburne. 



At the north base of the mountains, where the profile, descend- 

 ing from the mountains, passes from the upturned Devonian onto 

 Pleistocene till, which farther north is found resting on Lower Creta- 

 ceous, a belt several miles wide has been left blank, in view of the 

 possible occurrence of Carboniferous and Lower Mesozoic rocks 

 between the Devonian and the Cretaceous; and similar contact gaps 

 have been left in other parts of the section. On topographic grounds, 

 however, it seems probable that the Mesozoic and Carboniferous 

 formations are absent at the above point on the Anaktuvuk, having 

 been removed by erosion, and that the inland edge of the Lower 

 Cretaceous or Jura-Cretaceous may rest directly on the Devonian, 

 as indicated in fig. 4. Areas away from the route traversed, where 

 the geology is unknown, are also left blank; while, on the other hand, 

 general geologic information and the probable occurrence of certain 

 formations are represented by notes printed in red. East of the 

 geologically colored portion of the map the notes applying to the 

 region lying north of the Arctic Circle are based on the work of the 

 writer in a previous year, a while those to the south of the Circle, on 

 the west, and along Alatna and Kowak rivers in the region of the 

 sixty-seventh parallel are by Mr. W. C. Mendenhall, geologist in charge a.~ 



of the Kowak expedition, whose work* has just been published. g, 



aSchrader, F. C, Reconnaissance along the Chandlar and Koyukuk rivers, Alaska: Twenty-first Ann. Rept. U. S. 

 Geol. Survey, pt. 2, 1900, p. 448. 



SMendenhall, W. C, Reconnaissance from Fort Hamlin to Kotzebue Sound, Alaska: Prof. Paper U. S. (Jeol. Survey 

 No. 10, 1902. 



T?>&.i 



