74 O. W. Tyrrell — Alkaline Igneous Rocks, West Scotland. 



Glasgow, is a typical example. This rock has been often described, 

 first by Teall,' later by Macuair,* and finally a complete account has 

 recently been given by Bailey.^ Hence it is unnecessary to describe 

 the rock in this place. It seems appropriate to designate this common 

 and widespread variety of tesclienite as the Glasgoiv type since it was 

 first described by Teall from the Glasgow occurrences. The mineral 

 composition of the Lugar teschenite, given in column II, Table III, 

 may serve as the quantitative definition of the Ghisgow type, as it is 

 practically identical with tlie Necropolis Hill rock. 



The contact facies is a black basaltic lock consisting microscopically 

 of a fine-grained holocrystalline aggregate of plagioclase, augite, olivine, 

 and analcite, frequently with abundant biotite and red Jiornblende. 

 The ferro-magnesian minerals, especiully olivine and biotite, are 

 distinctly more abundant than in the coarse central facies, and the 

 rock takes on a lamprophyric habit. If occurring as an independent 

 mass it would doubtless be assigned to the camptonite group. 



Rocks of the Glasgow tj^pe are abundant in the east of Glasgow, 

 and also at Shettleston, still farther east. In Ayrshire they occur 

 near Old Cumnock, Skares, Lugar, Galston, Stewarton, Ardrossan, 

 and Troon. In Arran perfectly similar rocks are found intruding 

 the Triassic at Dippin Head.* Numerous occurrences of teschenite 

 from the Lothians have been described and some analysed.* 



A sub-variety of the Glasgow type occurs at Galston, Shettleston, 

 and elsewhere. It is characterized by the abundance of large pseudo- 

 porphyritic augite crystals and has a distinctive appearance in hand- 

 specimens. The large augites are set in a fine-grained groundmass of 

 plagioclase, orthoclase, and analcite, which is practically fi-ee from 

 ferroclase-magnesian minerals. A little biotite, olivine, and ilmenite 

 may be present. This rock may be referred to as the Galston type. 



A quite distinct variety of teschenite occurs in a group of sills 

 at Cathcart, near Glasgow. It is a fine-grained nepheline-bearing 

 rock which may be regarded as intermediate between the true 

 teschenites and the theralites of the Barshaw tj'pe (p. 80). It 

 consists of plagioclase, titanaugite, olivine, red hornblende, analcite, 

 nepheline, and ilmenite. Olivine is in greater and analcite in less 

 quantity than in the Glasgow type. Nepheline is fairly abundant in 

 broad plates which envelop felspars and flakes of biotite. In addition 

 tliis rock differs from the Glasgow type in the habit of tlie augite, 

 which occurs mostly in polysomatic groups of small subhedral grains. 

 This, together with the finer grain and the greater abundance of the 

 femic constituents, gives it quite a different aspect in thin section 

 to that of the Glasgow type. It may therefore be called the Cathcart 

 type. Similar rocks occur at the Linn Falls on the River Cart, near 

 Cathcart, the Glengyron railway cutting near Old Cumnock, and in 



^ Brit. Petrog., 1888, p. 194; see also pi. xiii. 



2 Trans. Glasgow Geol. Soc, vol. xlii, pt. i, pp. 79-82, 1907. 



^ Mem. Geol. Surv., Tlie Geology of the Glasgoiv District, 1911, pp. 114-16, 

 132-3. 



* Barker, Mem. Geol. Surv., Geology of North Arran, etc., 1903, p. 112. 



^ Mem. Geol. Surv., Geology of East Lothian, 1910, p. 114, and Geology of 

 the Neighbourhood of Edinburgh, 1910, pp. 293-301. 



