191 



micropegmatite and a rhombic pyroxene, this rock resembles certain 

 portions of the Whin Sill. A similar rock occurs at Kilsyth and Stirling. 

 Such rocks when they contain hypersthene may be conveniently termed 

 hypersthene-dolerites. 



A special type of rock occurs on the Island of Car Craig, near 

 Inchcolm, in the Firth of Forth (see Fig. 1, Plate XXII.). It is a medium 

 grained granular rock, largely composed of well formed prismatic crystals 

 of augite which may be recognized by the use of a hand lens. The other 

 constituents are felspar, often much altered, analcime, natrolite (?) 

 magnetite or ilmenite, a brown mica, and green decomposition products 

 giving aggregate polarization. The brown mica is especially common in the 

 most altered portions and often occurs as inclusions in the zeolites. It is 

 almost certainly of secondary origin. In thin sections the augite is seen to 

 be somewhat variable in colour, often assuming a marked reddish brown 

 tint, in which case it becomes decidedly pleochroic. A striking feature of 

 this rock is the abundance of analcime. Unless soda has been introduced 

 this would seem to imply the existence either of nepheline or a soda-lime, 

 rather than a lime-soda felspar. This rock possesses marked affinities with 

 the teschenites. 



In the district of West Lothian or Linlithgow basic lavas and tuffs 

 occur in the Calciferous Sandstone and Carboniferous Limestone. Their 

 total thickness is about 2,000 feet. The picrite of Bathgate, already referred 

 to, occurs in this district. There are also intrusive sheets in the Millstone 

 Grit and Coal Measures ; and east and west dykes, probably of Tertiary age. 



The contemporaneous volcanic rocks of the Stirlingshire district are 

 principally porphyrites and porphyrite-tuffs, like those of the Garlton Hills 

 in Haddingtonshire, and they belong to the same period, that is to the 

 Calciferous Sandstone series. There are also, according to Dr. GEIKIE, 

 " thick sheets of dolerite and other pyroxenic rocks which extend from 

 the neighbourhood of Kilsyth round the base of the Campsie Fells 

 to beyond Stirling. These masses have been intruded among the 

 Carboniferous Limestone strata, probably at a time before the consolida- 

 tion and disturbance of these strata, seeing that they have been faulted 

 and bent together with them. They belong to an extensive belt of 

 intruded matter which, keeping not far from the base of the Carboniferous 

 limestone series, extends to near the east end of the long county of Fife 

 and forms in its course the prominent eminences of the Cleish, Lomond 

 and Ceres Hills. We cannot be quite sure of the dates of these masses ; 

 some of them no doubt belong to the volcanic phenomena of the Car- 

 boniferous period, but some may be post-Carboniferous or even Tertiary." 

 Mr. ALLPORT says < x > : " South of the Kilsyth Hills there are several masses 

 of dolerite belonging to the intrusive sheets ; they occur at Croy, Gernal 

 Brae, near Over Croy, and at the foot of the hill a little south of Kilsyth. 

 Specimens taken from the above localities are almost imdistinguishable 

 from those collected at Ratho and West Craigs, near Edinburgh." 



We have already seen that the Ratho rock is, in places, a hypersthene- 



(1) Q.J.G.S. Vol. XXX., 1874, p. 561, 



