42G JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 17 



presentation of the driller's log. From the first-named log (the "percentage 

 log") it appeared that there are in this well distinct lithologic units charac- 

 terized by the proportion of the four ingredients differentiated, and that the 

 boundaries between these are usually well defined. From the second log it 

 appeared that these boundaries are usually marked by some distinct bed, some 

 times by a conglomerate or sandstone, but in most cases by a coarsely glauconitic 

 sandv bed. In this way it was possible to place the boundary between the 

 Marble Falls (Pennsylvanian) and the Lower Bend (Mississippian) with ab- 

 solute precision and in conformity with the paleontologic evidence. Boun- 

 daries between the Marble Falls, Smithwick, and Milsap were also suggested, 

 though in the absence of paleontologic evidence these are uncertain. Other 

 lithologic units not hitherto distinguished by names were indicated. It 

 was shown that the driller's log gives little if any evidence for the most sig- 

 nificant criteria. 



In further support of a hypothesis previously offered that unconformities 

 are marked by glauconitic beds it was shown that a glauconitic layer occurring 

 at the base of the Lower Bend just above the EUenberger limestone in out- 

 crops in San Saba County had been traced north through all wells (3) exam- 

 ined in which this contact appeared including the Seaman well more than 

 100 miles north of the outcrop. It was also indicated that pyrite or other 

 sulfides are associated with glauconite and phosphate at unconformities, 

 and it was suggested that the presence of all three minerals is due to the abun- 

 dance of organic matter encountered by a transgressing sea. 



T. Wayland Vaughan: Results of recent studies of the geology of the North- 

 ern West Indies. (Illustrated.) (Read by W. P. Woodring.) 



349th meeting 

 The 349th meeting was held at the Cosmos Club at 8 p.m., on Wednesday, 

 November 10, 1920. 



Informal Communication 



C. K. Wentworth: A sizing scale for the constituents of sedimentary rocks. 

 (Presented by M. I. Goldman.) 



Regtdar Program 



Courtenay De Kalb: The Rio Tinto and other historic mines of Spain. 

 (Illustrated.) 



C. W. GiLMORE: Remarks on the reconstruction of extinct reptiles. (Illus- 

 trated.) Laurence LaForge, Secretary. 



350th meeting. 

 The 350th meeting was held in the auditorium of the New National Museum 

 at 8 p.m., on Saturday, November 20, 1920. 



Regular Program 



Willis T. Lee: An evening "in the air." A popular presentation of the 

 use of aerial photographs in geography. 



Stereopticon views of natural scenery and of objects of geographic interest 

 as seen from an aeroplane were shown, including views of submarine ob- 

 jects and drowned land forms, shown here for the first time. There was also 

 a series of moving pictures taken from hydroplanes, showing scenes along the 

 Potomac, the Pacific fleet passing through the Panama Canal, and scenes 

 along the coast of California. The films were loaned for the evening by the 

 Navy Department. W. T. Thom, Jr., Secretary. 



