268 vaughan: correlation of tertiary formations 



BaO. 2Si02 is given in Gmelin-Kraut, where it is stated that a 

 mixture of that composition melts to a clear glass. ^ This obser- 

 vation was confirmed and the refractive index of the glass was 

 measured and found to be 1.606. 



J. W. French describes a crystal enclosed in " optical flint glass" 

 which is hexagonal and beautifully regular and shows ''stream 

 lines" about its edges. ^ From the general description I would 

 consider it possible that his crystal was identical with those of 

 barium disilicate here described were it not for the fact that he 

 noted no colors in polarized light. This may, however, have been 

 due to the extreme thinness of his crystals. It is true the glass 

 is called a flint glass which, in speaking of optical glass, means 

 a lead glass; but it is also stated that the source of the glass and 

 its composition are unknown. 



I am indebted to Mr. L. H. Adams for the photograph of the 

 glass specimen, to Mr. Olaf Andersen for a survey of the litera- 

 ture in search of previous information on barium disilicate, and 

 to Mr. G. W. Morey for calling to my attention the article by 

 French. 



GEOLOGY. — Correlation of the Tertiary geologic formations of the 

 southeastern United States, Central America, and the West 

 Indies.^ Thomas Wayland Vaughan, Geological Survey. 



The present paper contains tabular statements of the results 

 derived from prolonged investigations of the stratigraphic 

 equivalence of the Tertiary geologic formations in the South 

 Atlantic and Gulf Coastal' Plain of the United States, Mexico, 

 Central America, and the West Indies. The tables are excerpted 

 from two larger papers I now have in course of publication, 

 referred to in the foot-note below,- but as the two papers men- 



^ Gmelin-Kraut, Handbuch der Anorganischen Cheinie, 3^: 237-238. 



* Trans. Optical Soc. 16: 224. 1916. 



1 Published by permission of the Director of the U. S. Geological Survey. 



^ Vaughan, T. W., The biologic character and geologic correlation of the sedi- 

 mentary formation of Panama in their relation to the geologic history of Central 

 America and the West Indies. U. S. Nat. Mus. Bull. 103 (in press); Cenozoic his- 

 tory of Central America and the West Indies. Geol. Soc. Amer. Bull., vol. 23 

 (ready for press). 



