1903-4.] Mr J. G. Goodchild on Intrusive Bocks. 225 
which formerly occupied the vapour-cavities of the lavas have 
been converted by subsequent thermo-metamorphism into various 
forms of Epidote and the associated zeolites into Albite or other 
felspars. These are common effects in the areas that have been 
affected by thermo-metamorphic action. 
But some of the most striking cases of the development of 
minerals by the causes which have given rise in adjacent areas 
to eruptive masses of deep-seated origin are to be found in the 
case of the metamorphic marbles which occur in various parts 
of the Highlands of Scotland and elsewhere. Referring 
to the specimens in the Scottish Mineral Collection, I find 
the following species occurring within the substance of these 
altered limestones : — Quartz, Andesine, Anorthite, Tremolite, 
Diopside, Forsterite, Biotite, Phlogopite, Sphene and Apatite, 
besides Graphite, Idocrase, Garnet, Zoisite, Wollastonite, and a 
variety of other minerals with which at present we are not 
concerned. The feature of special interest in these cases is the 
development within the limestone by the same causes to which 
the formation of eruptive rocks is due (whatever that may be), of 
an assemblage of rock-forming minerals which are either identical 
with those which characterise rocks of eruptive origin, or else are 
allied to them. Amongst these are Quartz, two felspars (or more 
than two) ; Tremolite, as a representative of the Amphiboles ; 
Diopside and Wollastonite as representatives of the group to which 
Pyroxene belongs; Forsterite, which is closely allied to Olivine; 
two micas (perhaps three), and other rock-forming minerals. Yet 
no one seems to doubt that these minerals have been developed by 
metamorphic changes out of impurities which occurred within the 
marble. But it does not matter in the present connection whether 
the limestone was impure to begin with, and contained in those 
impurities the substances required for making the silicates referred 
to, or whether part of these requisites may have been introduced 
into the rock through the agency of the thermal waters which 
have been concerned in bringing about the final result. Any way, 
the fact is one of great importance in the present connection, and 
must on no account be allowed to drop out of sight. 
PROC. ROY. SOC. EDIN. — YOL. XXV. 
15 
