﻿part 2] 



PICEITE-TESCHENITE SILL OF. LIT GAR. 



117 



suite, and is present in all the rocks except the peridotite. It 

 occurs in small amount in the theralites, although unrecorded in 

 the Tables. "Where present in notable quantity its amount varies 

 from 30 to 40 per cent, (allowing for the presence of nepheline) in 

 the lugarites, to an average of 15 per cent, in the teschenites. 

 Nepheline occurs in measurable amount only in the theralites (up 

 to 16 - 6 per cent.), but is almost certainly present in small quantity 

 in the teschenites and lugarites. Titanaugite is the most abundant 

 and constant mafic mineral of the suite. It averages about 30 

 per cent, in the teschenites, increases to 36 per cent, in the thera- 

 lites, and attains its maxinrani development, 556 per cent., in an 

 augitic variety of picrite. Red soda-hornblende (barkevikite) is 

 absent from the teschenites, save in a domafic schlieren (Table I, 

 No. 5, p. 103), but is present in amounts ranging from 8 - 6 to 29 - 5 per 

 cent, in all the other rocks, the latter amount occurring in veins of 

 lugarite devoid of titanaugite. Olivine averages about 10 per cent, 

 in the teschenites and theralites, is absent from the lugarites. and 

 attains its maximum development in the peridotite, where it may 

 form 70 per cent, of the rock. Biotite averages about 3 per cent, 

 in most of the types, and is most abundant (6 '7 per cent.) in the 

 hornblendic variety of the theralite. Iron-ore is most abundant in 

 the teschenites, averaging about 7 per cent., but dwindles steadily 

 downwards tlnmigh the sill, although it is never entirely absent. 

 Apatite is a comparatively abundant and constant constituent. It 

 averages about 1 per cent, throughout the sill, is absent from the 

 peridotite, and is most abundant in the lugarites, thus illustrating 

 its association with analcite. 



The mineralogical variation with depth in the sill m&y be shown 

 by means of a diagram (fig. 5, p. 116). For this purpose it has 

 been found advisable to average the types (see Table VII, below), 

 thus smoothing over minor mineralogical irregularities. 



Table VII. 

 Modes of Rocks in the Lugar Sill. 





1. 



2. 



3. 



4. 



5. 



6. 



7. 



8. 



Plagioclase (AbjAii! to 



23-2 



27-9 



31-7 



28-6 



19-9 



12-6 



2-9 





Ab 2 An 3 ). 



















Orthoclase 



10-2 



5-6 



1-4 



47 











Analcite 



16-1 



19-9 



14-7 



16-3 











Nepheline 



Titanaugite 











14 V 6 



J 457 



11-1 





28-1 



27-2 



33-6 



30-6 



36-0 



10-8 



41-4 



20-5 



Barkevikite 











6-1 



23-4 



10-6 



io-o 



Olivine (serpentine) ... 



10-6 



7-5 



8-7 



8-9 



13-6 





30-1 



65*2 



Biotite 



3-4 



1-5 



25 



2-5 



5-2 





0-2 



2-0 



Iron-ores 



7-1 



9-3 



6-8 



7-5 



3'3 



3-8 



30 



2-3 



Apatite 



1-3 



ri 



0-6 



0-9 



1-3 



3-7 



0-7 





Felsic constituents 



49-5 



53-4 



47-8 



49-6 



345 



58-3 



14-0 



0 



Mafic constituents 



505 



46-6 



52-2 



50-4 



65"5 



41-7 



86-0 



100 



1. Upper teschenitn (Table I, 1) ; 2. Analcitic teschenite (Table I, 2) ; 3. Lower 

 teschenite (Table I. 3, 4) ; 4. All teschenite, except melanocratic variety of 

 Table I, 5 (Table 1, 1, 2, 3, 4) ; 5. All theralite (Table III, 1, 2) ; 6. All lugarite 

 (Table III, 3, 4) ; 7. All picrite (Table V, 1, 2) ; 8. Peridotite (Table V, 3). 



