Sortas—On the Variolite and Associated Igneous Rocks. 1112 
or 703°6 volumes of olivine and enstatite give rise to 990 volumes 
of serpentine, an increase of 40 percent. The extrusion of serpen- 
tine from altered olivine into cracks in the surrounding minerals 
and the larger fissures of the whole rock becomes thus readily intel- 
ligible. 
Turning now to the amesite molecule we perceive that its deri- 
vation from pyroxenic material involves great destruction of the 
pyroxene, as is shown in the following :— 
Pyroxene. Amesite. 
[ Si0(0,Mg) },$i,0,(0,Al),+20H, = Si(OMgO0H),[0A1(OH), |(0A10) 
+ 4§810,. ida 
The molecular weight of the pyroxene in the equation is 482; and 
if the specific gravity be taken as 3°25, a very probable estimate, 
we arrive at 150 for the value of the molecular volume. Since the 
molecular volume of the resulting amesite is 110, we have here a 
loss of 40 volumes or 26°7 per cent. If, however, the volume of 
liberated silica be included in the account, the loss becomes a gain ; 
we cannot assign a less volume to this than 90, and consequently 
on the total transaction there will be an expansion of 150 volumes. 
to 200, or a gain of 33:3 per cent. 
Since amesite, so far as we know, is never the sole chloritic 
product of the hydration of pyroxene, it will be more instructive 
to consider examples in which both serpentine and amesite molecules 
are produced together; thus the volume of pennine (Sp;At,) is 
6:78 per cent. less than that of the pyroxene which furnishes it, and 
of clinochlore (SpAt) 10 per cent. I must confess to having felt 
some little surprise at this result, since the general diffusion of 
chlorite in diabase and other hydrated basic rocks would naturally 
have led one to expect the chlorite to possess a larger volume than 
the pyroxene from which it is derived; but though this is clearly 
not the case, there is evidently great expansion when the total 
change involving the liberation of silica is considered. If the 
volume of clinochlore and quartz be compared with that of the 
pyroxene from which they result, a total expansion of 34 per cent. 
will be found; and since the clinochlore may be assumed to be at 
least as soluble as the silica, we may suppose that the surplus 
volume (34 per cent), which is carried away in solution, will 
