The Breadalbane Mines. 203 



decomposition products, and contains much brown biotite 

 interspersed through the matted mass of beautifully striated 

 plagioclase crystals, which, with some augite, magnetite, and 

 occasional crystals of pyrites, make up the main portion of 

 the rock. It may be provisionally named Kersantite or 

 Micadiorite, till a more extended investigation shall disclose 

 its true relationship. 



It extends upwards from the shore of Loch Tay at 350 feet 

 to the 900-feet contour, and has in turn been pierced by a 

 rock of totally different character, veins of which ramify in 

 countless multitudes through the older mass. The later rock 

 is of pink colour, and the thinnest threads can be easily 

 detected in the sombre Kersantite with which it is sharply con- 

 trasted. It is well seen on the beach a short distance west- 

 wards from the old smelting works, where it is exposed in 

 mass, while further inland it is only represented by dykes 

 and strings appearing at places where the rock surface has 

 been laid bare. So far as we have observed, it never passes 

 out of the Kersantite into the surrounding schists, as Thost 

 asserts in his paper on the Breadalbane Mines. He states 

 that the " porphyry " extends some three miles southwards 

 of Tomnadashan, but has apparently confounded this rock 

 with quartz-porphyry, dykes of which occur at places in the 

 neighbourhood, but have no connection with the rock in 

 question. It is a granitoid rock largely composed of pink 

 orthoclase, with quartz, greenish brown mica, and some plagio- 

 clase interspersed through it. The character of the mica and 

 the presence of plagioclase leads us to class it under the 

 variety of granite known as " granitite," but sometimes the 

 orthoclase crystals are very , large, when it passes into a 

 species of granitic porphyry. Both rocks are probably very 

 ancient, but have been injected into the schists at a period 

 subsequent to the time of their metamorphism. 



3. Distribution of Ores. — Small quantities of pyrites are 

 disseminated throughout the basic rock, but the ore appears 

 to be developed chiefly at places near the junction of the 

 two rocks, or, in other words, the injection of the acid rock 

 into the basic seems in some way to have influenced the 

 original distribution of the metallic minerals. The ore is 



