MERIDEN MUD VOLCANO. 77 



4. A variety of the volcanic rock characterized by the large number of 

 minute perfectly round steam holes which are commonly in pairs or in 

 two conjoined spheres forming a " figure of eight" section. This indicates 

 that the rock was solidified near the moist mud, from which bubbles es- 

 caped rapidly, and that it congealed rapidly and without motion. The 

 base is a dark gray, slightly brownish glass filled with a fine brown dust 

 concentrated around cavities and crystals. It contains rarely an angular 

 grain from the sandstone, showing that it w T as consolidated during the 

 upward passage of the muddy water and then shattered. The glass 

 swarms with feldspar microlites. There are also a few small feldspar 

 rods and a single colorless pyroxene ciystal (see plate 9, figure 4). 



5. Another fragment of a slightly different glass has pores which are 

 long, multilobate, and parallel, thus showing sluggish motion. These 

 two are almost the only cases of steam holes in the glass breccia. 



Chemical Discussion. 



In his article on the lavas of the Sandw T ich 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 tachylites, and only that of Ostheim in 

 Hessen, with its green superficial color and liver brown interior color, 

 resembles these glasses. I have not seen any anatysis 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 structure, and druzy surface. 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 IVJr H. N. Stokes, of the United States Geological Survey, was 

 made on the pure liver brown glass from the large mass at the top of the 

 bed on the south path. It has specific gravity of 2.87 and melts easily 

 to a black magnetic and frothy glass (see plate 8, figures 4 and 5) : 



Basic Pitchstone from "Ash Bed" northeast of Meriden. 



Si0 2 46.86 



Ti0 2 1.13 



C0 2 2.19 



P 2 3 15 



F trace. 



A1 2 3 13.96 



Fe 2 3 . 5.23 



* 



Neues Johrbuch fur Mineralogie, vol. lviii, p. 57. 



