04 PROCEEDINGS OF THE CORDILLERAN SECTION 



The meeting then adjourned for lunch, reassembled, and was called to 

 order at 2 p. m., and the following papers were presented : 



GYPSUM AND ANHYDRITE FROM THE LUDWIG MINE, LYON COUNTY, NEVADA 



BY AUSTIN F. ROGERS 



(Abstract) 



At the Ludwig copper mine in eastern Nevada a large gypsum deposit out- 

 crops on the surface. On the 400-foot level gypsum and anhydrite occur side 

 by side. The gypsum has been formed from the anhydrite by hydration. The 

 anhydrite was probably formed by the evaporation of a closed basin or arm of 

 the sea. 



Presented without notes ; illustrated by diagrams. Discussion by J. C. 

 Jones, who suggested that the anhydrite was probably formed from orig- 

 inal gypsum at the time of the intrusion of the granodiorite. Further 

 discussion by Louderback and Weber. 



TRACHYTIC PERLITE FROM LONE HILL, NEAR SAN JOSS, CALIFORNIA 



BY G. E. POSTMA 



(Abstract) 



A dark-gray perlite vitrophyre makes up a low dome-shaped hill about half 

 way between San Jose and New Almaden. This rock contains about 70 per 

 cent of silica, and on account of the absence of quartz it is classed as trachyte. 

 Its place in the quantitative system will be determined by a chemical analysis. 



Presented from manuscript, and illustrated by drawings. 



FLUTING OF CRYSTALLINE ROCKS IN THE TROPICS 

 BY J. C. BRANNER 



(Abstract) 



Photographs of the Serra Riscada and of other peaks in the interior of the 

 State of Ceara, Brazil, show fluting on a gigantic scale. The rocks are homo- 

 geneous crystalline rocks resembling coarse-grained granodiorites. The region 

 is hot and arid and the rainfall highly concentrated. 



Presented without notes. Discussion by Lawson, and further discus- 

 sion by Branner. 



INFLUENCE OF WIND ON THE ACCUMULATION OF OIL-BEARING ROCKS 



BY J. C. BRANNER 



(Abstract) 



Marine diatoms appear to have been the source of the petroleum and allied 

 deposits of Calif omia. The diatomaceous shales of California are not strictly 



