322 JIESSRS. A. HAKKEK AND J. E. MARK ON 



Probably more than one lime-silicate is present. The dominant 

 one gives the interference-colours of a pyroxene, and has marked 

 cleavage-traces, parallel to which it extinguishes. This may be 

 referred with some doubt to wollastonite. It is partly collected in 

 crystalline patches and streaks, but smaller granules of the same or 

 a similar mineral make up a large part of the rock, in conjunction 

 with a clear substance polarizing in grey tints and occasionally 

 showing the twinning of felspar. In the pyroxenic patches occur 

 grains of a yellow opaque mineral, probably pyrrhotite. Here and 

 there among the pyroxene is seen a little grain of calcite, showing 

 that here, at 600 yards from the granite, the elimination of the 

 carbonic acid is not quite complete [1225]. 



In hand-specimens this rock has a compact homogeneous appear- 

 ance, with a pinkish-grey or pale violet colour, and a hardness 

 rather less than that of orthoclase. The specific gravity of an 

 average specimen is 2*874, which agrees with the identification of 

 the chief constituent as wollastonite. The pale violet colour figures 

 frequently in descriptions of foreign lime-silicate rocks. 



Specimens of the Middle Coldwells taken at a point S.S.W. of 

 Wasdale Old Bridge show a similar compact porcellanous appear- 

 ance, but with a light grey colour. They resemble very closely the 

 Upper Coniston Limestone of Wasdale Head, but have a rather 

 higher density, 2*899, owing, as the microscope shows, to a larger 

 proportion of pyroxene. The dominant mineral here is the colour- 

 less lime-augite, which is largely developed, in crystal-plates en- 

 closing the felspar, &c. in ophitic fashion [1306, 1307]. At this 

 locality, about 460 5'ards from the probable outcrop of the granite, 

 there is no longer any trace of calcite remaining. It would appear 

 that, in these impure calcareous rocks, the particular lime-silicates 

 produced vary from point to point, as determined, perhaps, by com- 

 paratively slight differences in the chemical composition of the mass. 

 Some light is thrown on the conditions governing the formation of 

 augite, wollastonite, &c., by Vogt's * interesting researches on 

 slags. 



An interesting feature in the Packhouse Hill section is a meta- 

 morphosed fault-breccia, which intervenes between the Lower and 

 Middle Coldwell beds. The lowest beds seen here in the Middle 

 division are ordinary flags, but there appears to have been a lower 

 calcareous band similar to that described above, for fragments of the 

 characteristic pale-violet rock occur in the breccia, mingled with 

 pieces of the dark flags and vitrified-looking fragments of the under- 

 lying grit. The whole is united by a greenish finely- crystalline 

 cement of pyroxene. 



The fragments of grit appear in sections as a mosaic of clear 

 crystal-grains of quartz and felspar, evidently of metamorphic 

 formation. It is impossible to estimate the proportions of the two 

 minerals, but a fair number of the grains show twinning and seem 

 from their properties to be orthoclase. No repeated twinning is 

 observed [1286, 1287]. Among the grains of the mosaic, and 



* Arch. f. Math, og Naturvidensk, vol. xiii. (1890) pp. 34-71, Christiania. 



