108 



PROCEEDINGS OF THE ACADEMY OF 



[1894. 



but whether it is augite or not is at present uncertain. A fragment 

 weighing 2.459 grams in air, and 1.297 grams in distilled water had 

 a specific gravity of 2.11, evidently far too low for lava as generally 

 known, undoubtedly due to the extremely porous nature of the ma- 

 terial. By producing a coarse powder and taking the specific gravity 

 in a picnometer, the result is 2. 85. 



Considered from a chemical standpoint, this lava is decidedly 

 basic, as the quantity of silica determined analytically was 48.55 

 per cent. 



The specific character of this rock, now shown in the form of stalac- 

 tites is that of the so-called vesicular basalt. 



On some of these volcanic stalactites, there had formed a thin 

 layer of colorless crystals so small that their form could be recog- 

 nized only under power. These 

 thin prismatic crystals are attach- 

 ed to one end and terminated by 

 short pyramids; on certain faces 

 they are longitudmally striated. 

 In the groups are frequently seen 

 twin crystals whose dual faces 

 are mostly the longer axis. Fig- 

 ure 1, magnified about 4 diame- 

 ters, shows how the crystals are 

 attached to the volcanic stalac- 

 tites. A slide, prepared and ob- 

 served under a power of about 

 45 diameters shows the twin- 

 formations of the crystals. Fig. 

 2. That these crystals belong 

 to the monoclinic system is evident 

 from the fact of their inclined ex- 

 tinction which, upon measure- 

 ment, was found to be 37°, the 

 longer axis of the crystals being 

 zero to extinction over the pyra- 

 mid. The colors of polarization 



were brilliant. Dichroism was 



Fig. 1. Volcanic stalactite covered , . i • . i , n „„ 



with sclenite, x 4. unnoticed ni these forms. 



With the aid of Toulet solution the specific gravity of the material 



