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sheet to sheet, described above, are replaced by a peculiar 
breccia zone. 
The character of this breccia zone which may be more 
than two hundred meters thick is best seen from the photo- 
graph, (Pl. ХИ). The rock consists of immense blocks of nau- 
jaite in a network of lujavrite veins; a detailed description is 
given (p. 37). The breccia is evidently an igneous breccia; as 
proved by its flow structure it has originated at a time when 
the naujaite was solid and the lujavrite semi-fluid, but since the 
lujavrite shows no noticeable diminution in the size of its grains 
towards the contacts with the naujaite, the latter must have 
been hot when the breccia was formed. 
It can hardly be doubted that the formation of this breccia 
was due to the same local subsidence which gave the concave 
form to the batholitic sheets, and the subsidence, thus, must 
have occurred after the consolidation of the naujaite and during 
the crystallization of the lujavrite. This view is corroborated 
by the fact that the schistose structure of the main mass of 
the lujavrite — a structure produced before the final consoli- 
dation of the rock (see p. 166) — is parallel to the general 
concave benching of the batholite; while the lujavrite along the 
eastern vertical walls of the batholite, where it has apparently 
been forced upward by the subsidence of the central portion, 
is characterized by an almost vertical schistosity. 
It may be asked why the breccia zone cannot have ori- 
ginated from magmatic stoping. The character of the breccia 
indeed is in some respects about such that might be expected 
of a true ‘stoping breccia’. But there are also considerable dif- 
ferences, viz.: 
1. The lujavrite, as mentioned above, shows no noteworthy 
diminution in size of grains at its junction with the naujaite. 
2. The upper surface of the lujavrite is on the whole con- 
cave, while the upper surface of a stoping magma, as a rule, 
must be convex. 
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