88 bowen: significance of glass-making processes 



occasionally a small rounded quartz grain. More often the 

 quartz grains are inclosed by the phosphate pebbles, whose sur- 

 faces are frequently pitted with cavities, suggesting the possible 

 removal of some mineral. Some cavities in several of the peb- 

 bles examined were filled with vivianite. In no specimens of 

 the vivianite examined were there indications of inclusions of the 

 brownish-yellow ocherous material, but some of the vivianite 

 crystals showed irregularities of surface similar to embayments 

 which we believe resulted probably from external interference 

 of the ocher on crystal growth. 



ORIGIN OF THE VIVIANITE 



The vivianite from the Florida locality is of secondary origin, 

 formed we believe by the action of ferrous-iron solutions on the 

 phosphate. Although rated at the present time as a rare mineral 

 in the land pebble phosphate deposits, the conditions certainly 

 appear to be favorable to a more general formation and distri- 

 bution of the mineral in these deposits. 



PETROLOGY. — The significance of glass-7naking processes to 

 the petrologist. N. L. Bowen, Geophysical Laboratory. 

 (Communicated by A. L. Day.) 



The entry of the United States into the war was the occasion 

 of an enormously increased demand for optical glass to be used 

 in all kinds of military instruments. The supply of glass from 

 abroad was almost completely cut off. In the effort to meet 

 the demand by domestic production many problems were met 

 with for whose solution the advice and assistance of scientific 

 men seemed desirable. Glasses are, for the most part, silicate 

 'mixtures that have been melted at a comparatively high tem- 

 perature and then cooled to the glassy state. Since the prin- 

 cipal activity of the Geophysical Laboratory has been the study 

 of the behavior of silicates at high temperatures, it was expected 

 that the experience of that organization might be of material 

 assistance, and its services were therefore called upon. I was 

 one of the several sent to the glass plant of the Bausch and Lomb 



