proceedings: geological society 309 



THE GEOLOGICAL SOCIETY OF WASHINGTON 



The 307th meeting was held in the lecture room of the Cosmos 

 Club on March 22, 1916. 



informal communications 



E. T. Wherry presented a communication on the cavities in vein 

 fillings of the basalt near Paterson, New Jersey. He showed that 

 the lozenge-shaped cavities from a shale in eastern Pennsylvania 

 were like those in the basalt. These cavities correspond to glauberite 

 crystals. (Published in full in Journ. Wash. Acad. Sci. 6: 181-184. 

 1916.) 



REGULAR PROGRAM 



R. B. Sosman and J. C. Hostetter: Zonal growth in hematite and 

 its bearing on the origin of certain iron ores. 



In studying the natural oxides of iron, the authors have observed 

 that some of these can be separated magnetically into fractions. They 

 have also shown (Journ. Ainer. Chem. Soc, April, 1916) that ferric 

 oxide (Fe 2 3 ) and magnetite (Fe 3 4 ) form a series of solid solutions in 

 which the percentage of FeO increases continuously from zero to 31.03, 

 which is the percentage in magnetite. The oxides become increasingly 

 magnetic as the percentage of FeO increases. 



The powdered oxide from certain crystals of hematite from Elba 

 contains considerable FeO and can also be fractionated magnetically. 

 It is therefore not homogeneous, as would be the case if the crystal 

 were a uniform solid solution throughout. Analyses and magnetic 

 measurements on a cross-section of an Elba crystal showed that the 

 magnetic susceptibility and percentage of FeO vary, not irregularly, 

 but continuously, being highest at the base and lowest at the free- 

 growing tip of the crystal. The crystal is therefore zoned with respect 

 to its FeO content. The physico-chemical conditions which could 

 bring about such a zonal growth were discussed. 



R. W. Pack: Structural features of the San Joaquin Valley oil fields, 

 California. (Illustrated.) 



The general features governing the occurrence of oil in the San 

 Joaquin Valley are (1) the presence of material in which the oil origi- 

 nated; (2) an avenue affording an easy escape for the oil from this ma- 

 terial in which it originated; (3) lithologic and structural features 

 that together form a reservoir favorable for the accumulation of this oil. 



The first condition is satisfied by the presence of thick formations 

 of shale composed largely of the remains of minute organisms — dia- 

 toms and foraminifers — and it appears certain that it is in these forma- 

 tions and from these organisms that the petroleum originated. The 

 escape of the petroleum from these shales is rendered easy by the 

 unconformable relation at the top of the shales. Adequate reservoirs 

 are afforded by the sandy beds that rest upon the truncated edges of 



