270 O. II. Hershey — Belt and Pelona Series. 



conglomerate, No. 23, of my Nevada section. This would 

 place about (5,250 feet of sediments in the Belt series. The 

 lower members occur in a small area on the eastern slope of the 

 Egan Range about 10 miles north-northeast of Ely. On the 

 eastern slope of the same range about 4 miles north-northwest 

 of Warm Spring, the section extends down to No. 26. In a 

 belt extending from 5 miles north-northeast of Cherry Creek 

 to 9 miles south of that town, the section extends down to 

 No. 30. At Aurum, on the eastern slope of the Schell Creek 

 Range, No. 24 is exposed, but 15 miles farther south the sec- 

 tion extends down to No. 30. Nowhere is the base of the 

 Belt sediments exposed. All the granite seen in Eastern 

 Nevada is intrusive and probably post-Carboniferous in age, 

 except in the range west of Clover Valley, where, under a 

 limestone series, there were observed the following rocks : 



1. Light gray calcareous mica schist intruded by white mus- 

 covite pegmatitic granite. 



2. Gray mica schist. 



3. White, coarse-grained micaceous quartzite 



4. White micaceous quartz schist. 



5. Dark gray, coarse biotite gneiss and schist. 



6. Light grey granitic gneiss, varying to a slightly sheared, 

 fine-grained granite. 



7. Gray, medium-grained sheared granite. 



I have no doubt that these rocks are Archean in age. The 

 Belt series and a large part of the Paleozoic section are absent. 



Blackwelder, in the paper already cited, argues that the 

 Algonkian sediments in the Wasatch region were depos- 

 ited " chiefly by rivers on extensive plains in a climate which 

 was semi-arid or at least subject to dry seasons." He points 

 out that " the regularity of the dip and the small amplitude of 

 the cross-bedded structures implies currents moving in a single 

 general direction, and currents of water rather than of wind." 

 The ripple marks and tension cracks admittedly imply shallow- 

 water conditions, with frequent exposure of the mud flats. He 

 considers that " the imperfect assortment of the materials 

 appears to indicate that the sediments were deposited rapidly, 

 little time being given for that complete sifting of fine from 

 coarse debris which is characteristic of the work of waves upon 

 an open beach." He recognizes that the Algonkian (Belt) sed- 

 iments of Idaho were probably deposited under conditions 

 similar to those which obtained in the Wasatch region. Since 

 reading his paper, I have been endeavoring to consider the 

 rocks of the Coeur d'Alene District in the light of a possible 

 origin from meandering rivers upon a great delta plain,* but 



* Relative Geological Importance of Continental. Littoral and Marine Sedi- 

 mentation, part 3 ; Jour. Geol., vol. xiv, pp. 524-566, 1906. 



