D. Balsillie — Hypersthene Andesite, Fifeshire. 347 



marked intervals of quiescence more or less prolonged in the course 

 of their volcanic history. The prevailing dip of the rocks is towards 

 south-east, so that as we proceed in that direction progressively- 

 higher members of the sequence are encountered. As usual among 

 the igneous products of this geological period, the most abundant 

 extrusive types are andesites. More acid rocks, such as felsites, also 

 occur, but there is no evidence to prove conclusively that in the area 

 in question these are ever true lavas. (Reference may here be made 

 to the salmon-pink felsite of Lucklaw Hill, which has hitherto been 

 regarded as a lava. The enormous extension of this mass at right 

 angles to the general strike of the rocks and the manner in which it 

 sends ramifications into the andesites that surround it, especially on 

 its. northern boundaries, point only to one conclusion, viz. an 

 intrusive origin.) The andesites vary greatly in their physical 

 characters. Some are slaggy, having abundant mineral-filled 

 vesicles, others being thoroughly compact with a platy system of 

 joints and an occasional development of brecciation along their lower 

 portions. These latter compact rocks afford excellent material for 

 microscopic investigation, and as in many cases they have been laid 

 bare in quarries for the pi"o vision of material to macadamize the 

 public roads it is not difficult to collect representative examples of 

 the fresher types of the district. It is in reference to a fortunate 

 exposure in one of these artificial openings that this note has been 

 written, and the remarks that follow are based entirely on the 

 examination of rock specimens collected from one locality, viz. near 

 Pitcullo in East Fife. 



Inspection of a 1 inch to the mile topographic map of Fifeshire 

 will show that on the main road between the county town of Cupar 

 and Dundee there is, about 1 mile to the north-east of the little 

 village of Dairsie, a farm steading named Muirhead, from which point 

 a road runs west across the hills towards Craigsauquhar. Less than 

 half a mile along this road from the junction just mentioned, and 

 immediately on its right-hand side, a quarry has been opened among 

 the lavas. The main rock of the quarry, which is situated at no 

 great distance from the mansion bouse of Pitcullo, and is con- 

 sequently designated the Pitcullo Quarry, is not of such character as 

 to attract any special attention, but high on the worked face, on the 

 side remote from the road, a rock of remarkable freshness and with 

 a pitchstoue-like resinous lustre occurs. It is coated externally with 

 a light-brown crust, perhaps as much as a quarter of an inch in 

 thickness, but beneath this weathered zone is very black and 

 compact, and shows on a freshly broken surface abundant porphyritic 

 crystals of a glassy felspar. There is no line of demarcation between 

 this fresh rock and that lower in the quarry face, and the probability 

 is that it is merely a modification of the rock occurring there. 



Under the microscope confirmation of the fresh nature of the rock 

 is immediately to be obtained. It consists of a remarkably homo- 

 geneous, brown in colour, isotropic groundmass, in which are 

 disposed numerous porphyritic crystals of glassy felspar, ortho- 

 rhombic and monoclinic pyroxenes, as well as irregular grains and 

 irranules of raaunetite. 



