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



The condensed statement by Dr. Thomas sums up well the 

 chief characters of these rocks. But judging from my own 

 preparations the monchiquite type is as common as the 

 melilite-basalt. Since, however, the specimens are chance 

 chips and grains, the largest individual piece being less than 

 half a pea in size, which are mingled together between the 

 points indicated in the list of samples, there is no way of 



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Fig. 2. 



Biotite Monchiquite, Bermuda Is. 

 groundmass. Photo, by H. 



Large biotites in fine-grained 

 H. Thomas. 



definitely settling this point. 

 my own study of the lavas : 



The following are the results of 



Melilite-basalt. 

 The following minerals have been found in the sections : 

 iron ore, apatite, perovskite, angite, biotite, olivine, melilite, 

 orthoclase, nephelite, and analcite. The augite as a phenocryst 

 is usually well-crystallized with the forms «, (100) ; J, (010) ; 

 m, (110); and s\ (101); elongate on the vertical axis and 

 sometimes flattened parallel to a, (100). The largest embedded 

 crystal seen measured 4 mm along the b axis and half that per- 

 pendicularly. The regular cleavage is well developed. The 

 angle of extinction is large, c A c up to 45° or more, the bire- 

 fringence high. The color is brownish varying to olive and 

 as noted above there is often a deeper purplish border, recall- 



