442 D. Balsillie— 



Notes on the Doleritic Intrusions of East Fife. 



By D. Balsillie, F.G.S. 



rpHE following brief notes compiled mainly some years ago will, 

 -^ it is hoped, convey information supplementary to that provided 

 in the Memoir on the Geology of Eastern Fife (Appendix, pt. ii), 

 and are to be regarded as useful only where they furnish particulars 

 not already available from that source. 



The majority of the subsequently introduced igneous masses in 

 East Fife belong to one or other of the two great series of doleritic 

 intrusions that are now known to have such a wide distribution 

 in Central Scotland, viz. (a) Quartz-dolerites and (b) Olivine- 

 dolerites, including teschenites. The characters of these as developed 

 in this area may be set forth as follows : — 



(a) Quartz-dolerites. — Rocks of this type occur abundantly in 

 East Fife, and an admirable description of one, though by no 

 means the freshest member of the series, has been given by 

 Dr. Flett (vide loc. supra cit.). But the petrographic details of 

 the quartz-dolerites have now in other areas ^ been so thoroughly 

 ascertained that it would be merely a repetition of familiar fact 

 to elaborate these at length here. In the field there is a singular 

 lack of uniformity in the character of these masses. Some are 

 dark, fine-textured, and thoroughly basic looking, whereas others 

 are coarse-grained and carry an abundance of pink felspar. 

 Segregation veins and patches are characteristic of the quartz- 

 dolerites, and another feature, one indeed almost of diagnostic 

 value, so far at all events as the intrusive igneous rocks of East Fife 

 are concerned, is the remarkably constant presence of a considerable 

 content of iron sulphide either in the form of pyrite or marcasite. 



Microscopically, the quartz-dolerites consist essentially of lime- 

 soda felspar ranging up to a fairly basic labradorite or bytownite, 

 orthoclase, generally in comparatively small amount, monoclinic 

 pyroxene, sometimes two monoclinic pyroxenes — clino-enstatite and 

 augite, and hypersthene. These minerals are enclosed in a highly 

 felspathic or quartzo-felspathic groundmass that often shows 

 micropegmatite. The latter varies greatly in amount, sometimes 

 being present in such quantity as to confer upon the rock a distinctly 

 porphyritic character. In addition to the foregoing constituents, 

 the quartz-dolerites contain as accessory ingredients hornblende, 

 biotite, iron ores, and apatite. An ophitic structure is occasionally to 

 be observed, but is in general not characteristic of rocks of this type. 



The segregation veins are of two kinds, " blue bands " and " red 

 bands ", the latter often coarser in texture, but apart from colour 



I See Sir J. J. H. Teall, British Petrography, 1888, p. 190 ; also J. D. Falconer, 

 Trans. Rov. Soc. Edin., vol. xlv, 1906, p. isS ; P.^Macnair, Trans. Geol. Soc. 

 Glas., vol.'xiii, 1907, p. 56 ; G. W. Tyrrell, Geol. Mag.. 1909, pp. 299 and 359 ; 

 Dr. J. S. Flett, Meyn. Geol. Surv. Scotland, " The Geology of the Neighbourhood 

 of Edinburgh," 1901. p. 301 ; and E. B. Bailey, Mem. Geol. Surv. Scotland, 

 " The Geology of the Glasgow District," 1911, p. 146. 



