D. Balsillie — Hypersthene Andesite, Fifeshire. 349 



found to amount from 40° to 45°, this corresponding with augite, 

 which I therefore take to be the monocliuic pyroxene present. 



Magnetite occurs disseminated as quadrangular and irregular 

 grains throughout the rock, and is frequently enclosed in the 

 pyroxenes. Apatite such as occurs in the Dumyat and Cheviot 

 andesites I did not observe. 



The groundmass of the PitcuUo rock examined under low powers 

 appears remarkably isotropic, but is resolvable under higher 

 magnification to a mass of little felspar crystals that lie in an 

 ultimate base of pale-brown or colourless glass with globulites. In 

 addition to the felspars, which are twinned on the albite law and 

 have only a small extinction angle, a second generation of pyroxenes 

 also occurs. Magnetite, too, is an abundant constituent. 



In sections of the Dumyat rock a number of lighter areas made up 

 of minute microlites and liaving a darker periphery were observed 

 by Dr. Flett. In their most perfect form these occur "as rounded 

 bodies which have some resemblance to spherulites". Such circular 

 aggregations of microlites I have not noted in the Pitcullo rock, 

 though irregular areas of a siniilar kind, and often with a darker 

 border, not uncommonly occur. Comparison, however, with hand- 

 specimens of the typical kugel andesite from Bath, Hungary, 

 convinces me that it would be quite unwise to describe kugel 

 structure as occurring in the Pitcullo rock. The Hungarian rocks 

 liave had a sort of pseudo-amygdaloidal structure conferred upon 

 them by the physically separable character of their kugels. This 

 certainly is not the case in the rock from East Fife. 



The rock that has now shortly been described is by far the freshest 

 typical andesite that I know in the district in which it occurs. 

 It is not, be it at once said, quite so glassy as the exceptionally 

 fresh rock from Dumyat, but in the best specimens is only a little 

 less so. 



The bulk of the material in the quarry consists, as has been 

 indicated, of hypersthene andesite, but is really a rock quite 

 different in appearance from that described in the foregoing notes. 

 It is grey in colour, is obviously in a much less fresh condition, and 

 suggests in no way, macroscopically at all events, relationship with 

 the fresh " pitchstone " that comes on top of it. Notwithstanding 

 this physical distinction, both appear to have belonged to the same 

 parent mass. Under the microscope the felspars can be seen to be 

 equally clear and glassy and to have an identical composition. Both 

 orthoihombic and monoclinic pyroxenes occur, as in the unaltered 

 rock, the former, however, now only represented by pseudomorphs 

 made up of strongly absorbing fibres. Impregnations and veins of 

 iron oxide are frequent, obscuring totally in some slices the real 

 nature of the rock tliat carries them. Tlie base is much less glassy, 

 and the felspars of the second generation are larger. It will there- 

 fore be seen that any distinction that occurs may only be due to 

 differences in the cooling history of the two portions of the rock and 

 to the fact that the glassy rock by virtue of its compactness has had 

 conferred upon it a higher degree of resistance to the agencies of 

 secondary change. 



