abstracts: geology 567 



GEOLOGY. — The physical conditions indicated by the flora of the Calvert 

 formation. E. W. Berry. U. S. Geological Survey Professional 

 Paper 98-F. Pp. 12, with illustrations. 1916. 

 This paper gives a summary of the small flora preserved in the Mio- 

 cene diatomaceous beds of the Calvert formation in the District of 

 Columbia and Virginia, and discusses its bearing on the physical con- 

 ditions of the Calvert epoch. It is concluded that the Calvert flora 

 was coastal flora of strikingly warm-temperate affinities, comparable 

 with the existing coastal floras of South Carolina and Georgia, or with 

 those along the coast of the Gulf of Mexico from western Florida to 

 eastern Texas. The climate of the Chesapeake Miocene epoch, cooler 

 undoubtedly than that of the Apalachicola or preceding epochs, was 

 neither cold nor cool-temperate. The age indicated by the Calvert 

 flora is middle Miocene. R. W. S. 



GEOLOGY. — Antimony deposits of Alaska. Alfred H. Brooks. U. 

 S. Geological Survey Bulletin 649, Pp. 64, with maps. 1916. 



Stibnite is widely distributed in Alaska having been found in 67 

 localities. In many of these it occurs simply as an accessory mineral, 

 but lodes have been found in the Fairbanks, Kantishna, Innoko, Idi- 

 tarod, Nizina, and Port Wells districts and on the Kenai and Seward 

 peninsulas in which stibnite forms the principal metallic mineral. 



The country rock of the stibnite lodes is sedimentary as a rule, but 

 differs greatly both as to age and lithology in the different districts. 

 Some deposits have been found in highly metamorphosed schists of 

 pre-Cambrian age. Others are found in little-altered elastics, as young 

 as Upper Cretaceous. Practically all the antimony lodes occur in 

 association with granular acidic intrusive rocks, among which the domi- 

 nating lithologic types have been described as quartz diorite and 

 monzonites. 



The Alaska antimony deposits may be classed in three principal 

 groups — siliceous gold-bearing stibnite lodes, stibnite-cinnabar lodes, 

 and stibnite-galena lodes. Of these the first two can be further divided 

 according to structure as fissure veins, shear-zone deposits, and stock- 

 works. 



The evidence at hand indicates that most of the stibnite deposits 

 were formed at a later time than the widespread epoch of Mesozoic 

 mineralization to which so many of the gold deposits have been assigned. 

 Formerly it was generally believed that nearly all the metalliferous 

 deposits of Alaska were associated with Mesozoic intrusives. It is 



