Notes on the Boleritic Intrusions of East Fife. 443 



there does not appear to be any principle that could serve to 

 discriminate them. Sometimes, either may consist of isolated 

 crystals of acid plagioclase enclosed in a groundmass entirely of 

 nncropegm.atite, ferromagnesian constituents being notably absent, 

 or they again may be discerned simply as a mosaic of quartz and 

 felspar, in part orthoclase, that encloses porphyritic crystals of 

 oligoclase and oligoclase-andesine, micropegmatite occurring only 

 as a frame round the latter and dying away into the surrounding 

 granular aggregate. On the other hand, the characteristic inter- 

 growth of quartz and felspar may be, and very often is, entirely 

 absent. Long needles of augite often occur in these vein rocks, 

 likewise shreds and larger fragments of hornblende and biotite. 

 Chemically, the veins are distinguished by their higher content 

 of silica and alkalies, showing at the same time a corresponding 

 diminution in lime, magnesia, and iron. Petrographically, as 

 pointed out by Dr. Flett, they are always cognate to the igneous 

 rock-bodies in which they occur. 



As regards the distribution of the quartz-dolerites in East Fife, 

 it may be said that they lie west of a line drawn south from near 

 Guard Bridge on the estuary of the River Eden to Leven on the 

 Firth of Forth. • East of this line the intrusions belong in general 

 to the olivine-dolerites, but it must be clearly understood that this 

 march is only intended to be approximate in its nature and applic- 

 able only to the area dealt with in the memoir. 



Some of the quartz-dolerites attain a great size in East Fife. 

 Thus the large sheet or sill that stretches south-west from near 

 Wemyss Hall covers an area of approximately 3 square miles, 

 and appears to be connected with another mass of no less extent 

 farther to the south-west. It is this intrusion that has involved 

 the outcrop of the Teuchats and Teasses limestone, and Sir Archibald 

 Geikie has given a section showing how the latter and associated 

 igneous rock have here probably been displaced by faultmg. What 

 relationship, if any, exists between the quartz-dolerite sills and the 

 similarly occurring masses of olivin.e-dolerite is not clear from any 

 field evidence in Fife known to the writer. 



{h) Olivine-dolerites. — These rocks as developed in the area 

 under review consist of felspar, monocliinc pyroxene, and olivine, 

 along with subsidiary and varying quantities of magnetite, ilmenite, 

 apatite, analcite, and zeolites. They appear as a rule to be in 

 a fresher condition than the corresponding masses south of the 

 Firth of Forth (e.g. the Gosford Bay dolerite), although rarely in 

 East Fife can it be said indeed that the felspars are quite unaltered 

 or the olivine without at least a film or sheath of serpentine. 



In East Fife the best road-metals appear always to be obtainable 

 from the olivine-dolgrites. But in this connexion it may be stated 

 that the freshest and most compact rocks do not always provide 

 the most expedient sources of supply ; for often the closest-grained 

 and apparently most resistant masses are those specifically rot 



