IGNEOUS GEOLOGY OE THE BATHGATE AND LINLITHGOW HILLS. 149 



differentiation has proceeded on lines similar to those described for closely allied rocks 

 by Teall, Harker, and Holland. The silica and alkalies tend to move inwards, and 

 the ferromagnesians outwards. Consequently, the interiors of the intrusions are more 

 acid than the margins. Where the differential movement has been local only, dark and 

 light coloured modifications are produced, which are contrasted both in mineral and in 

 chemical composition. 



Whether the whole of the silica percentage should be claimed as primary is, 

 however, open to question. The quartz, which is in intimate intergrowth with felspar, 

 is probably wholly original, although in places peculiar ragged portions of quartz occur 

 in the midst of linear micropegmatite and simulate very closely corrosion effects. Where 

 the quartz forms simple masses however, especially in the vicinity of vacuoles and 

 miarolitic cavities, some of it is undoubtedly of later origin. This is betrayed both by 

 the nature of its inclusions and the occurrence of ghosts of felspar crystals, as already 

 described, within the quartz. It is possible that this secondary quartz may be partly 

 of aqueous and partly of pneumatolytic origin. That both the lavas and the diabases 

 have been subjected to some extent to pneumatolytic action is fairly obvious. The 

 occurrence of bituminous knots in the lavas, and the extensive zeolitisation and 

 decomposition which some of them have suffered, are probably to be referred to such 

 action. In the diabases, also, fairly good evidence is obtained in the peculiar late 

 formation of pyrites in the ocelli and elsewhere.* It is just possible, therefore, 

 that the deposition of free quartz, as well as the kaolinisation and sericitisation 

 of the felspars and the amphibolisation and chloritisation of the augite, especially in 

 the neighbourhood of miarolitic cavities, may have been to some small extent the result 

 of the passage of steam and other gases through the porous rock after consolidation. 



4. Acknowledgments. 



To Prof. Jas. Geikie I am especially indebted for constant encouragement and 

 assistance during the preparation of these papers, and to Dr Horne for allowing me to 

 consult the original working maps of the Bathgate Hills. My best thanks are due also 

 to Dr J. S. Flett for much kindly criticism and advice, and to Dr J. W. Evans for 

 valuable assistance in petrological methods. Mr G. S. Blake of the Imperial Institute 

 has carried out the analyses for me, and numerous friends have helped me much by 

 their interest in my work. 



* See Weinschbnk, Grundziige der Gesteinskunde, vol. i. p. 118. 



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