354 INDEX TO THE STRATIGEAPHY OF NORTH AMERICA. 



A broad belt of metamorphosed sediments is shown on the map between Yukon and 

 Tanana rivers, and in this are known to be Devonian and Carboniferous and probably Silurian " 

 horizons.* Here, too, pre-Cambrian beds may be included. 



Schrader " has described a great complex of metamorphic sediments in which Carbonifer- 

 ous fossils have been found near the top of some doubtful Silurian forms in a limestone occurring 

 near the bottom. 



Mendenhall,'^ in his exploration of the Allen and Kobuk rivers, not attempting to differen- 

 tiate the semicrystalline rocks which he encountered in his rapid journey, grouped them 

 together under the term ' ' metamorphic complex." In this group are included schists of various 

 types, limestones, quartzites, and greenstones. The lithology is that of the older terranes of 

 other parts of Alaska, but Mendenhall was unable to ascertain the succession -within the com- 

 plex. The group was traced westward to Kotzebue Sound and was regarded by Mendenhall 

 in a broad way as the equivalent of the metamorphic terranes of Seward Peninsula. 



In Seward Peninsula the extremely complex structure, the great amount of 

 metamorphism, and the lack of detailed investigations have rendered any definite 

 statement of the stratigraphy impossible. Schists of different mineralogic compo- 

 sition are intricately associated with recrystallized limestones and basic intrusive 

 rocks, all much sheared. In different limestones at widely separated localities 

 fossils of Cambrian, Ordovician, Silurian, and Devonian or Carboniferous age have 

 been found, although most of the limestones have been too thoroughly recrystal- 

 lized to afford paleontologic evidence. There is strong probability that pre- 

 Cambrian sediments may also be included, but the lack of definite bedding and the 

 known occurrence of continued folds and thrust faults make the projection of dips, 

 and thus the interpretation of sequence, inconclusive. 



"■ Prindle, L. M., Fairbanks and Rampart quadrangles, Yukon-Tanana region, Alaska: Bull. U. S. Geol. Survey 

 No. 337, 1908, pp. 18-23. 



I> In 1909 Silurian and Ordovician fossils were found in the A\Tiite Mountains, in the Fairbanks quadrangle, by 

 Prindle and identified by Ulrich. 



" Schrader, F. C, Reconnaissance in northern Alaska: Prof. Paper U. S. Geol. Survey No. 20, 1904, pp. 55-72. 



<2 Mendenhall, W. C, A reconnaissance from Fort Hamlin to Kotzebue Sound: Prof. Paper U. S. Geol. Survey 

 No. 10, 1902, pp. 31-36. 



