484 'T. W. E. DAVID, W. F. SMEETH, AND J. A. SCHOFIELD. 
Now certain members of the scapolite group are the only 
minerals with which we are acquainted which entirely satisfy the 
conditions, and on these grounds we think it highly probable that 
such a mineral is present. 
The question of the pre-metamorphic condition of a schist, such 
as the present one, is of great interest, but unfortunately little 
can be done towards its elucidation from mere hand specimens. 
One or two suggestions may, however, be made. From the bulk 
analysis this mica schist appears to have the composition of an 
acid igneous rock so far as its more stable constituents (SiO, and 
Al,0;) go. In other constituents there are important differences. 
For example, the amount of CaO and of Mg0O is largely in excess 
of, and the amount of alkalis falls far short of, that usual in acid 
igneous rocks. Now this diminution of the alkalis and increas? 
of the alkaline earths is suggestive of denudation and sedimenta- 
tion, and lends colour to the suggestion that this rock may be 
metamorphosed sediment. 
Again the numerous tourmalines present indicate, probably, 
thermal metamorphism under the influence of an highly heated 
acid rock from which boric acid and fluorine might be derived. 
(In the granulitic aplite No. 4, we have evidence of the presence 
of such an igneous mass—containing much tourmaline—in the 
district). One may therefore suggest with some probability that 
this mica-schist has been previously a sedimentary rock which has 
taken its present form under the influence of a neighbouring 
mass of highly heated acid magma. 
B,—Sprctmens From Posszession IsianD. 
Amygdaloidal Trachyte, (No. 9). 
Grey in colour with numerous irregular cavities, many of which 
are filled with yellowish and white materials. The texture 
uniform, giving in section a mass of small lath-shaped felspat 
which appear to be sanidine and oligoclase. Between these there 
is a fair amount of colourless glass containing magnetite and very 
minute grains of highly-refracting greenish material, probably 
Jy 
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