696 



PROCEEDINGS OF THE OTTAWA MEETING 



and as yet even reconnaissance mapping lias been carried over only about one- 

 fifth of the territory. Those familiar with the conditions met with by the 

 geologist in this field need not be reminded that they are by no means favor- 

 able, and this will account for the rather meager results of some of the ex- 

 plorations. It appeared desirable to gather the very incomplete data and to 

 attempt to outline the areas of some of the larger stratigraphic subdivisions, 

 and this has been done on this map. The blanks in the map represent unsur- 

 veyed areas, yet the colored parts do not by any means indicate results of 

 equal reliability. Areas like the Seward peninsula and the Copper River basin 

 have been surveyed in considerable detail, while others, like the Kuskokwim 

 and Tanana valleys, have been covered by only the most hurried reconnaissance 

 work. 



Stratigraphic Subdivisions and their Description 



Ten stratigraphic subdivisions have been made ; seven are sedimentary, two 

 igneous, and one metamorphic. The so-called Pelly gneisses include gneisses 

 and crystalline schists, as well as more massive intrusives, and possibly some 

 sediments, which may in part be Archean, but very likely are, for the most 

 part, deformed igneous rocks of a later date. A group of highly altered sedi- 

 ments, embracing many different formations, and probably chiefly Paleozoic, 

 occupies the largest areas in the province. . The areas of Silurian are small, 

 because it is only where fossils have been found that they could be differ- 

 entiated from the other metamorphic terranes. The incomplete data has made 

 it necessary to throw the Devonian and Carboniferous into one group. In 

 most of the field it has been found impossible to make any subdivisions in the 

 Paleozoic which are included in the metamorphic group. 



Though all the subdivisions of the Mesozoic have been recognized in Alaska, 

 the data are too fragmentary to permit of mapping them separately, and only 

 two groups are recognized. The one embraces the Triassic and Jurassic, as 

 well as the undifferentiated Mesozoic, and the second the Cretaceous. 



The Tertiary, undifferentiated on the accompanying map, is almost entirely 

 Eocene, for Miocene and Pliocene beds have been found at a few localities. 



The Quaternary coloring has been extended to only the larger areas. Most 

 of the rivers, except those that traverse the Coast range, are bordered by 

 Pleistocene silts and gravels. 



Of the intrusives the scale of the map permitted the representation of only 

 the larger stocks, and even these have been omitted in the Archean areas where 

 the gneisses and igneous rocks a*e not always easily differentiated. The dis- 

 tribution of the larger areas of the recent and Tertiary volcanics is shown 

 throughout the regions surveyed. 



It has been impossible to avoid the crazy-quilt effect due to the fragmentary 

 data, yet some of the larger features of the geology are well illustrated. The 

 general northwest trend of the western cordillera continues into Alaska to 

 about the one hundred and forty-eighth meridian, where it bends abruptly to 

 the west and southwest, as if to meet the northeastern extension of the Asiatic 

 continent. That this is but a topographic reflecion of the dominant structural 

 lines is well illustrated on this map, where you will note that there is a marked 

 change of strike along the central meridian of Alaska. This line, in fact, 

 marks the transition from the American to Asiatic trend of bed-rock structures. 



