On the Genesis of Some Scottish Minerals. 213 



arrangement, which results in the formation of Kyanite, 

 Staurolite, Andalusite, Fibrolite, Cordierite, Biotite, some 

 Garnets and Pyrites. Secondary enlargements of felspars 

 and Quartz are due to the same cause. 



Graphite, which probably represents, in this case, carbon- 

 aceous matter originally diffused through sediments, is 

 developed in the form of fine scales in some of the rocks 

 in the contact zones around the Galloway granites. There 

 are good specimens of these in the Scottish Mineral Collec- 

 tion, from near Creetown. Very similar graphite schists, 

 probably due to much the same cause, occur on certain 

 horizons in the Highland Metamorphic Series. 



Anthracite occurs in Scotland under two forms, both 

 of which are here regarded as connected with the uprise 

 of heated waters. The commonest, well represented by the 

 oft-described coal-seam at New Cumnock in Ayrshire, has 

 originated in situ, probably through the action of heated 

 alkaline waters connected with the formation of a contiguous 

 intrusive mass. The other case is well represented by the 

 Anthracite found in the Lower Carboniferous tuffs of the 

 Calton Hill, near Edinburgh, and in the (possibly) Tertiary 

 agglomerates so well displayed on the shore of the Forth 

 between Elie and St Monance. These occurrences of 

 Anthracite may well be due, in the first instance, to the 

 formation of metallic carbides, which, by subsequent chemical 

 changes, have been converted into purer carbon. I have 

 elsewhere ventured to suggest that even the Diamond may 

 have been formed in this way. 



Where arenaceous matter forms the predominant con- 

 stituent, the number of minerals developed appears to be 

 inversely proportionate to the purity of the rock. Calcareous 

 impurities may give rise to some of the minerals above 

 mentioned under " limestone," and argillaceous matter may 

 be rearranged so as to form some of the minerals mentioned 

 in the last paragraph. Pure quartz-sand remains nearly 

 as originally deposited ; the grains, at the most, undergoing 

 mere secondary enlargement through the deposition of silica 

 derived from beds on a hioher horizon. The conversion of 



