3 02 REGINALD A. DALY 



violence of the explosion. More generally, the nodules occur in 

 projectiles largely composed of the normal trachydolerite. The 

 specific gravity of one ellipsoidal nodule about 8 cm. in length was 

 found to be 3.316; it is almost entirely free from feldspar. 



The nodules inclosed in lava are best displayed in the frost- 

 riven felsenmeer surrounding the summit pond. One of these was 

 sectioned and specially studied. The plagioclase was found to 

 have the composition of acid anorthite, Ab t An 9 . A few small 

 tables of the feldspar and rare granules of olivine are inclosed 

 in the diallage, but in general, the anorthite is interstitially 

 developed between the olivine and diallage crystals, which seem 

 to have crystallized nearly simultaneously and after the iron ore. 

 The pyroxene is much more often idiomorphic than is the olivine. 

 The specific gravity of this nodule is 3 . 1 1 1 . 



The Rosiwal method afforded the following estimate of its 

 weight percentages: 



Olivine 62 



Diallage 26 



Anorthite 11 



Magnetite and ilmenite 1 



100 

 Assuming the olivine to have the same composition as the 

 olivine in the lava flow of 1852, and the diallage to have the aver- 

 age composition of basaltic augite, 1 the nodule was calculated 

 to have, approximately, the composition shown in column 1 of 

 Table V. 



TABLE V 



1 See Journal of Geology, XVI (1908), 410. 



