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14-19. The St. Peter appears to have been derived from a relatively 

 low land mass to the northward. This land is believed to have sloped 

 southward, in which direction its rivers flowed, to have been affected 

 by a moderately humid climate, but not to have been clothed with 

 vegetation, because land plants had not yet developed. The land 

 included pre-Cambrian crystalline rocks and a broad fringe of Potsdam 

 sandstone. 



20. The derivation of the St. Peter, largely from this Potsdam belt in which 

 the sands were already well assorted and rounded, together with the added 

 sorting and rounding by wind work in the supply area, and by waves in the 

 sea, explains in a wholly satisfactory manner the high degree of purity and 

 rounding of its grains. 



21. These sands were deUvered to the sea both by rivers and to a minor 

 degree directly by winds, and were distributed chiefly by waves and currents. 



22. The shores of this sea were fluctuating, but during middle and late 

 St. Peter time, were for the most part north of the Iowa-Minnesota Une. 



23. North of that line there is quite probably a small amount of St. Peter 

 that is truly unmodified terrestrial deposit. . . . 



24. South of the Iowa-Minnesota line, conditions of both transportation 

 and deposition were almost wholly marine, and in this area there did not exist 

 during any part of St. Peter time, a great interior desert of drifting sand. 



A discussion of the geographic conditions under which this and other 

 early Proterozoic formations were made, closes the volume. 



R. D. S. 



Deposits of Manganese Ore in Arizona. By E, L. Jones, Jr., and 



F. L. Ransome. Bulletin 710-D, United States Geological 



Survey, Government Printing Office, Washington, D.C., 1920. 



Pp. 92, pis. 6, figs. 8. 



The production of manganese ore as such in Arizona dates from 



1915. The producing district Hes in the more southern part of the state. 



The greater part of the ore worked bears at least 35 per cent manganese, 



and not more than 4 per cent iron. The ore is shipped east to Illinois, 



Alabama, Tennessee, and Pennsylvania, and lately also to CaHfornia. 



Perhaps the chief difficulty encountered in production lies in the inacces- 



sibiHty of the mines to railroads, which necessitates "packing" the 



manganese out of the mining district, a tedious and expensive process. 



Various scattered manganese have been studied by Mr. Jones in the 



preparation of this paper. Dr. Ransome describes those at Bisbee and 



Tombstone. In the latter district, the sequence extends from the 



pre-Cambrian Pinal schist through Cambrian, Devonian, Mississippian, 



