E. B. Bailey d^ G. W. Grabham — Plagioclase Felspars. 255 



most of this latter has probably been carried off in solution as calcium 

 carbonate. 



Permo-Carboniferous Intrusions. 



These rocks are quartz dolerites, occurring as sills and dykes ; in 

 composition and age they agree with the well-known Whin Sill of 

 Northumberland. Albitization is a very widespread phenomenon 

 among these intrusions, e.g. in the North Queensferry Sill (12,181). 

 It presents the same features as have just been described in connection 

 with the lavas, only here there is a much greater development of 

 finely divided white mica. 



The interesting feature of the Scotch Permo-Carboniferous intrusions 

 in connexion with the problem of albitization depends upon the fact 

 that they carry numerous short irregular segregation veins very rich in 

 alhite. These are of two classes, described by Falconer ' as ' red ', or 

 ' iron band ' and ' blue band ' respectively. 



Aualysed by 

 Analysed 



A. Blue band, from quartz dolerite, Carriber Quarry, Linlithgow, 

 G. S. Blake, quoted from Falconer. 



B. Red band, from quartz dolerite, Kettlestoun Quarry, Linlithgow, 

 by G. S. Blake, quoted from Falconer. 



C. Soda-aplite, from quartz gabbro, St. David's Head, Pembrokeshire. Analysed 

 by A. V. Elsden, Q.J.G.S., 1908, vol. Ixiv, p. 284. 



There is no very satisfactory sliced material of blue band in the 

 Survey collection, but the red bands (13,777, 12,181) are clearly seen 

 to be pink felspathic veins, carrying a fair amount of quartz, with 

 a small proportion of accessory minerals. The felspars, which are 

 seldom free from white mica, occur in neat laths, with trachytic 



^ "The Igneous Geology of the Bathgate and Linlithgow Hill": Trans. Hoy. 

 Soc. Edin., 1906, vol. xlv, p. 133. 



