﻿part 2] 



PICRITE-TESCHENITE SILL OP LUGAR. 



129 



of gravity in the settling of olivine-crystals has only been appealed 

 to in the case of Lugar, although its effects are clearly demonstrable 

 in the other sills. 



EXPLANATION OP PLATES X & XL 



( The slide numbers are those of the collection in the Geological T><3partment, 

 University of Glasgow.) 



Plate X. 



Pig. 1. Slide R.1045. X 24. Ordinary light. Upper contact of teschenite, 

 Bellow Water, above Bellow Bridge, Lugar. A felt of minute felspar- 

 laths and grains of augite, with magnetite, and a little interstitial 

 analcite. Note numerous variations of granularity and banding 

 within a small compass. (See p. 95.) 



2. Slide E1044. X 12. Ordinary light. Analcite-rich teschenite, 



upper band, Bellow Water, above Bellow Bridge, Lugar. Labra- 

 dorite, augite, and analcite, with numerous flakes of biotite and 

 skeletal ilmenite. Note the central area of analcite with alteration 

 proceeding from the margins. (See p. 98.) 



3. Slide PV 249. X 12. Ordinary light. Theralite, augite-rich variety, 



light-grey patch below the contact of theralite with teschenite, 

 Bellow Water, Lugar. This rock is rich in a beautiful lilac- 

 coloured augite with darker margins. Fresh olivine occurs in 

 small grains about the centre of the field. The turbid interstitial 

 material consists of labradorite and nepheline. (See p. 105.) 



4. Slide PV 161. X 24. Ordinary light. Hornblende-theralite, Bellow 



Water, Lugar. Swarms of minute augite-grains are poikilitically 

 enclosed in a comparatively-coarse ground-mass of labradorite (clear) 

 and nepheline (turbid). Abundant pseudo-porphyritic olivine and 

 barkevikite. The grain of this rock appears deceptively fine, owing 

 to the granular augite. (See p. 105.) 



Plate XI. 



Pig. 1. Slide PV 164. X 12. Ordinary light. Lugarite, vein in picrite, 

 Glenmuir Water, Lugar. Large prisms of barkevikite, labradorite 

 (white), ilmenite, and interstitial turbid analcite. This field con- 

 tains much more felspar than the normal type of lugarite. (See 

 p. 107.) 



2. Author's slide. X 12. Ordinary light. Picrite, south of the railway 



viaduct, Glenmuir Water, Lugar. Consists mainly of augite and 

 olivine, with interstitial turbid analcite, labradorite, and a little 

 barkevikite. 



3. Slide E, 155. X 12. Ordinary light. Hornblende-peridotite, Glen- 



muir Water, Lugar. Consists mainly of olivine partly serpen- 

 tinized, with granular augite, and large poikilitic plates of barkevikite. 

 Note that the augite has the same habit as in the theralite. (See 

 p. 111.) 



4. Slide E. 1085. X 12. Ordinary light. Lower contact of teschenite, 



Glenmuir Water, Lugar. Note the varying granularity and the 

 number of different bands within a very small distance. The coarse 

 white band is a later vein of teschenite. (See p. 95.) 



Discussion. 



The President (Dr. A. Harker) congratulated the Author 

 on having found so interesting a subject of investigation. His full 



