IGNEOUS GEOLOGY OF THE BATHGATE AND LINLITHGOW HILLS. 137 



possible to establish a sequence, the lower lavas there being doleritic and more' acid, 

 the higher basaltic and more basic. Elsewhere, doleritic and basaltic flows are irregularly 

 intermingled. # 



2. The Contemporaneous Intrusions. 



These are the product of the same period of igneous activity as the lavas. They 

 include both doleritic and basaltic types, but present few features of general interest. 

 The rock of Mochrie's Craig and Peace Knowe is remarkably decomposed with produc- 

 tion of much kaolin, calcite, serpentine, and analcite. It varies much in texture from 

 point to point, and in places assumes a spotted character from local aggregations of 

 ferromagnesians. 



3. The Later Intrusions. 



Introduction. 



The diabases of later age occur (l) in a series of E.-W. dykes of no great breadth 

 crossing almost at right angles the outcrops of the various lava zones ; and (2) in a 

 series of rudely columnar intrusions of dyke-like and laccolitic habit, elongated in a 

 N.-S. direction, and occasionally of considerable thickness. A genetic relationship with- 

 out doubt exists between the two. Their petrographical similarity, first pointed out in 

 a classic paper by Sir A. GEiKiE,t has been fully established on more detailed study, 

 and it is impossible to resist the conclusion that the dykes and sills are the products of 

 the same distinct period of igneous activity. Their age alone still remains rather 

 doubtful. Sir A. Geikie, on the assumption that the E.-W. dykes were of Tertiary age, 

 was of opinion that the sills also should be referred to that period. Of late years, how- 

 ever, doubt has arisen as to the Tertiary age of the dykes, while, on the other hand, sills 

 in Eastern Fife of a similar character to those in the Linlithgow area have been referred 

 almost certainly to late Palaeozoic times. Hence it is possible to consider of Palaeozoic 

 age all the material possessing the same peculiar structure found in the basin of the 

 Forth, whether it occurs in dykes or in sills. In the Bathgate Hills, however, no 

 positive evidence has been found apart from the fact that some of the smaller faults, 

 themselves probably late Palaeozoic, displace the long sinuous intrusion of the Eaven Craig. 



The central portions of the dykes and sills are very coarse-grained, and to the eye 

 evidently composed of a granular mixture of a grey or pink felspathic and a dark green 

 ferromagnesian constituent with black lustrous iron-ore and a considerable amount of 

 pyrites. In the smaller intrusions the rock is homogeneous throughout, but in the larger 

 dykes, and especially in the sills, a local differentiation is very common into a darker 

 coloured variety in which augite is more abundant than felspar, and a lighter coloured 

 variety in which felspar evidently predominates. J In the latter, the ferromagnesian 



* The Tuffs accompanying the lavas have not been investigated in any detail. For a short description of these, 

 see Geikie, Trans. Roy. Soc. Edin., vol. xxix., 1880. 



t A. Geikie, Trans. Roy. Soc. Edin., vol. xxxv., 1896, p. 21. 



% Cf. "The Geology of Eastern Fife," Geol. Sur. Mem., 1902, p. 190. 



