G. W. Tyrrell — Alkaline Igneous Bocks, West Scotland. 77 



I. Fine-grained banded tesehenite, near upper contact, Bellow Water. 



II. Tesehenite, with abundant analcite, near upper contact, Bellow Water. 



III. Melanocratic tesehenite, below II. 



IV. Theralite, below III. 



V. Hornblende-theralite, below III. 



VI. Augite-picrite, top of ultra-basic mass, Glenmuir Water. 



VII. Olivine-picrite, top of ultra-basic mass, Glenmuir Water. 



VIII. Hornblende-peridotite, main ultra-basic mass, Glenmuir Water. 



IX. Tesehenite, between base of peridotite and X, Glenmuir Water. 



X. Tesehenite, lower contact, Glenmuir Water. 



Whilst some of the rocks from the upper contact contain nepheline, 

 the theralite zone, so conspicuous in the Lugar sill, is absent. 



Another picrite-teschenite complex is intruded as an intricately 

 ramifying mass into the agglomerate of the Carskeoch vent, near Patna. 

 Among the rocks represented here are picrite, tesehenite, lugarite, 

 monchiquite bearing huge crystals of hornblende and biotite, and 

 essexite. Ultra-basic couches occur in the interior of some of the kylite 

 sills, and will be described later under the head of kylite (see Part II). 



4. Lugarite. — A very remarkable rock with affinities to the leuco- 

 cratic teschenites and to the ijolites occurs in the heart of the Lugar 

 teschenite-picrite complex as a sill about 4 feet thick, and as thin 

 veins or dykes penetrating the picrite. In hand-specimens it has 

 a very striking appearance. It generally shows a grey or greenish- 

 grey groundmass crowded with lustrous blaik prisms of barkevicite 

 ranging up to 3 inches in length, and frequently arranged in rude 

 stellate groups. Shorter and stouter black crystals occur which are 

 recognizable as augite. In thin section the rock is seen to be 

 composed of analcite, nepheline, plagioclase, barkevicite, titanaugite, 

 ilmenite, and apatite. The analcite (with nepheline) forms about 

 50 per cent of the rock, and is usually decomposed with the formation 

 of a brown dust. It maybe recognized by the fact that it occasionally 

 clears to a limpid patch of undoubted analcite, and by the frequently 

 complete analcitization of the enclosed felspars. Titanaugite and 

 barkeyicite occur as large euhedral crystals, the extraordinarily perfect 

 forms of which testify to the freedom of their crystallization, and the 

 liquidity of the magma in which they were developed. The augite is 

 of a deep-purple colour with an intense pleochroism ; the barkevicite 

 is red brown, also with strong pleochroism. In the prevailing variety 

 of the rock titanaugite occurs to the extent of 20 per cent, and 



