BY H. C. RICHARDS. 139 



completion of the matrix perlite in the quartz, nor perlites 

 iormed in the quartz and completed in the matrix as 

 described by Watts.-*' Sometimes, however, perlitic cracks 

 surround the crystals. 



In the hand-specimen this pitchstone bears a very close 

 resemblance to one described by Harker-^ from Glas 

 Bheinn Mhor in Skye, and it is a matter of difficulty to 

 distinguish between them. 



When the analysis is recalculated to 100 per cent, 

 after removing' the water and is compared with the recalcu- 

 lated analysis of the Mount Barney rhyolite a very close 

 ]-esemblanee is seen, so that they in all probability have 

 a coirTiion source. (S^-'e Table VII.) This is of interest 

 as tlie rocks are so different in texture and in addition 

 are separated by several miles. 



Ehyolitcs intermediate hetiveen the suh-alkaline and alkaline 



varieties. 

 Specimen 233. — Localitj^ : Portion 28v, parish of Biarra. 

 This light- grey rock forms a hill on the west side of 

 the railway line, just near the Ottaba railway station. It 

 is a lithoidal variety, but has occasional phenocrysts of 

 anorthoclase set in a hypohyaline groundmass which con- 

 tains very fine equigranular quartz and orthoclase. Good 

 • fiuxional arrangement is shown through the rock in places, 

 and the weathered surface often shows a ropelike structure 

 owing to the twisting of the viscous magma when extruded. 

 Through the rock, one sees under the microscope indefinite 

 green granules which are difficult to determine. This 

 rock is much richer in soda than potash. The specific 

 gravity is 2-61. Name: Rhyolite. 



Specimen 234. — Locality: Glen Eock, Esk. This is 

 a light brown in colour, and it forms the large mass of 

 Glen Rock. It is remarkably free from phenocrysts 

 although occasionally one sees crystals of sanidine which 

 are slightly larger than the rest of the mass. The rock 

 is hypohyaline, and the grain-size is very fine being about 

 •075 mm. The fabric shows a very poor fiuxional arrange- 

 ment, and there is a tendency for the felspar laths to 



'Q.J.G.S., 1. (1894). 

 ' Skye Memoir, p. 408. 



