248 HENRY S. WASHINGTON 



t 

 A leucite-tephrite from Mte. San Antonio is described by 

 vom Rath,' which seems to be more like the Conca tephrite than 

 the other just described. Megascopically only few phenocrysts 

 of augite, leucite and feldspar are visible, while under the micro- 

 scope the groundmass resembles that of many leucitites already 

 described. Sanidine phenocrysts are few, but smaller ones of 

 plagioclose are abundant. Vom Rath's analysis is inserted here : 



100.01 



Leucite -trachyte. — The occurrences of this rock which I 

 observed seemed to belong to the second (trachytic) phase of 

 the volcano, though on this point I cannot speak with certainty. 

 My specimens may be referred to two different varieties, an 

 augitic and a biotitic. To the former belongs the rock of a well 

 marked flow at Acqua Rotta, about a kilometer and a half north- 

 west of Teano. The groundmass of this is very compact and 

 fine grained, and of a dark gray color. Leucite phenocrysts are 

 not abundant, but many small black augites and a few flakes of 

 biotite are visible. Under the microscope a few large leucite 

 sections met with are clear, with quite strong double refraction, 

 and show few inclusions. The pale green augite phenocrysts are 

 clear, carry inclusions of magnetite, especially toward the edges, 

 and generally show corroded outlines. The biotites present are 

 all altered to an almost opaque, finely granular mass of augite 

 and magnetite, generally to such an extent that but little of the 

 original mineral remains. The groundmass resembles that of 

 many leucitites, being composed largely of small round leucites, 



leucite show out with striking clearness against the background of bright anorthite 

 between crossed nicols. 



' Vom Rath, op. cit. 243. 



