IGNEOUS GEOLOGY OF THE BATHGATE AND LINLITHGOW HILLS. 143 



augite, and is occasionally found aggregated into little clumps. When fresh it is pale 

 brown in colour, and faintly pleochroic to a very pale green, and otherwise closely 

 resembling the rhombic pyroxene in the Ratho diabase.* The mineral appears to be 

 near bronzite, the pleochroism not being sufficiently marked for hypersthene. Usually 

 the bronzite is more weathered than the augite with which it is associated, and is 

 partially or wholly replaced by a fibrous bastite. (See PL II. fig. 6.) In many sections 

 may be observed short rectangular or eight-sided pseudomorphs in serpentinous and 

 chloritic minerals which may be after bronzite, but which, in view of the peculiar habit 

 of the augite described above, should probably be more properly referred to monoclinic 

 pyroxene. In many dykes, however, and also in the sills, there occur pseudomorphs of 

 a ferromagnesian mineral in a micaceous substance resembling iddingsite. These occur 

 in long rectangular and eight-sided sections, which have much more the habit of rhombic 

 pyroxene than of olivine. Frequently undecomposed remains of pyroxene are found 

 within the pseudomorph, and these sometimes extinguish straight and sometimes oblique. 

 Further, true augite is occasionally found with a border of the same compact, intensely 

 pleochroic material. It is probable that these secondary formations are pseudomorphs, 

 both after bronzite and after ordinary augite rich in magnesia. It is interesting to note, 

 also, that wherever monoclinic augite is found decomposing in this way, the portions 

 still undecomposed have a faint but distinct pleochroism similar to that of the 

 bronzite. 



Olivine, completely serpentinised, is found everywhere on the margins of the dykes 

 and sills, but only very rarely in the interiors of the smaller dykes, and not at all in the 

 central portions of the sills. Its place appears to be taken in the coarser rocks by 

 rhombic pyroxene of somewhat similar composition. Where both bronzite and olivine 

 are wanting, their Mg-content is probably included partly in the augite and partly in 

 the ilmenite. 



Apatite is very abundant, and builds long slender needles, frequently continuous 

 through several crystals of felspar, augite, and quartz. One or more axial canals, filled 

 with glassy material in the form of negative crystals, are fairly common. Ilmenite or 

 titaniferous magnetite is everywhere abundant, and occurs in the form of large, compact, 

 or thin detached and parallel plates, or in open porous crystals. In the central portions 

 of the sills it frequently builds elongated skeletal forms, round which the columnar 

 augites have grown in such a way as to simulate a pegmatitic intergrowth. Late 

 crystallisations of iron-oxide like that described by Monckton t have not been recog- 

 nised with any certainty. Pyrites is common throughout, and occurs usually in the 

 form of irregular masses and porous cubes, and frequently in a granular condition in 

 the cracks and cleavages of felspar and augite, and has evidently been one of the latest 

 minerals to crystallise. J (See PL II. fig. 1.) 



* Teall, British Petrography, 1880, p. 163. 



t Monckton, " The Stirling Dolerite," Quart. Journ. Geol. Soc, vol. li. p. 48. 



X Of. Vogt, Zeitschrift fiir praktische Geologie, April 1893, fig. 27. 



