> ELISHA MITCHELL, SCIENTIFIC SOCIETY. 63 
tating closely a simple combination of a prism of one order 
aud a pyramid of the other in the tetragonal system. The 
apparent prismatic faces are formed for the most part by 
the pinacoid faces, 4, but the crystals interpenetrate each 
other somewhat irregularly so that portions of the base 
c, 001, coincide with 4, fg. 1. The lines of twinning on 
the pinacoid faces between 4 and / twinned are generally 
regular, while those between 4 and cand also those which 
cross the prism faces vz, 110 (the apparent pyramid) are 
generally quite irregular. The 0 faces do not show the 
striations parallel to the edges 6 and a. which, meeting 
along the twining lines, often reveal the complex nature 
of such crystals, nor were any reéntrant angles observed 
parallel to the edges of the apparent prism as are common 
on phillipsite and harmotome. 
Fig. 2 represents another habit of the crystals where 
m, 110 is wanting and a, 100 is in combination with 6, 
O10. The method of twinning ts similar to that already 
described, but the crystals being terminated by a, 100 
instead of wz, 110 show prominent reéntrant angles at 
their ends. These crystals are very similar to those of 
_-harmotome from Bowling near Dumbarton on the Clyde, 
ie ee a Bs 5 8 le Cll 
Ps 
described by Lacroix.* 
The only forms that were observed were a, 100; 6, 010; 
¢, 001 and mw, 110, with e, 011 only as twinning plane. 
‘The faces of the crystals are somewhat rousded and 
*Bull. de la Soc. Min. de France, No. 4, p. 94, 1885, 
