332 L. V. Pirsson — Geology of Bermuda Island ; 



of these rocks that I quote from it freely, with reproductions 

 of two of his photographs, aud then present additional observa- 

 tions of my own : 



"It would appear that the igneous rocks are mostly, if not 

 entirely, lavas of the alkali group, and that they fall under two 

 main heads. 



a Feldspar-free basalts, including melilite-basalt. 



b Lavas of monchiquitic and lamprophyric affinities. 

 Judging by the fragments and powders it seems that the basaltic 



Fig. 1. 



Fig. 1. Melilite-basalt, Bermuda Is., 1045-1075 feet. Shows zoned 

 augite and altered olivine in an augite, melilite groundniass. Photo by 

 H. H. Thomas. 



rocks are in excess of other types, but the lamprophyric and 

 monchiquitic ones appear to predominate in the upper 100 feet of 

 the igneous rocks, occur at depths of 1045-1075, 1140, and their 

 presence is suggested at various positions in the basaltic types. 



The Basalts. — Inferred solely from the powders these are com- 

 pact, dark gray rocks consisting of a deeply colored augite and 

 fresh and decomposed olivine as microporphyritic crystals set in 

 a base of some feldspathoid mineral. Feldspar appears extremely 

 rare and it is evident that most of the rocks are free from it. 



Two fragments of the basalts, from 1045-1075 feet, were large 

 enough to furnish sections and both proved to be melilite-basalt. 

 The microscope reveals the fact that the microphenocrysts con- 

 sist of olivine and augite while the matrix is composed of a later 



