436 GEOLOGY OP OLD HAMPSHIEE COUNTY, MASS. 



filling for a considerable distance along one or more sides, leaving a film 

 of the black sand grains attached, and then a more Hmpid feldspar has 

 gi-own in the narrow cavities thus formed. 



CONTACT MATERIAL. 



A slide cut within the porous outer portion of the trap from the 

 contact of one of the bomblike masses of trap with the glass-breccia 

 showed only a very feldspathic and vesicular diabase. Specimens cut 

 from the fused border between the two showed a rock with the aspect of 

 an augite-andesite. The well-shaped feldspars of two generations and the 

 equally well-shaped olivines were inclosed in an opaque red-brown base, 

 which in thinnest places revealed its hyalopilitic or fibrous stnictiu-e. 

 (PI. VIIIc, fig. 5, p. 430.) Its outer sui-face had at times a rounded and 

 lobed, fused surface, and just under the surface a single row of steam holes 

 filled with siHca, all indicating a superficial remelting. 



LITHOPHYS^. 



In one large specimen from near the base of the bed north of the 

 quany at Greenfield the breccia was full of well-formed lithophysfe a hah" 

 inch to an inch and a half in diameter. The cavities were half filled with 

 cm-died masses of a lighter rock. 



CHEMICAX DISCUSSION. 



In his article on the lavas of the Sandwich Islands and other volcanic 

 islands of the Pacific,^ Cohen states that all the basic glass found was 

 anhydrous, and in general a basaltic pitchstone has not been described. 



I have studied slides of many tachylytes, and only that of Ostheim, 

 in Hessen, with its green supei-ficial color and liver-brown interior color, 

 resembles these glasses. I have not seen any analysis of this rock giving 

 water determination. It is deeper brown than most of the glass here 

 studied, and contains large, round, oval spherulites with still deeper color, 

 with radiate structm-e, and di-usy sm-face. The other basaltic obsidians 

 quoted by Zirkel do not contain more than 2.75 per cent of water. 



The following analysis of basic pitchstone from the Meriden "ash 

 bed," by Mr. H. N. Stokes, of the United States Geological Sui-vey, was 

 made on a pure liver-brown glass identical with that here described. 



'Neues Jahrbuch fiir Mineralogie, Vol. LVin, p. 57. 



