161 
geological relations which indicate that the lujavritic magma — 
though present within the batholitic chamber at the same time 
as the magmas of most of the other rocks now constituting 
the batholite — has been the last to crystallize. That the two 
first-mentioned conditions would favour the formation of pure 
erystals of non-isomorphous minerals is evident. As to the 
influence of the temperature the experimental data are insuf- 
ficient in order to settle the question’; in the writer’s opinion, 
however, geological observations on the whole support the 
view, held by many authors’, that the homogeneous mixed 
crystals containing considerable amounts of both kinds of alkali- 
felspars only form at high temperatures and that a low temper- 
ature of crystallization favours the separation. 
The felspars of the ægirine-lujavrite also in other respects 
differ from those of the rocks described in the preceding pages: 
very often the larger among them are influenced by mechanical 
stresses. Thus many of the crystals are traversed by cracks 
or even bent, and not seldom strain-shadows may be observed. 
The latter phenomenon is especially common with the larger 
albite-crystals in which also the distribution of the twin-lamelle 
has been influenced by the formation of the cracks. The dyn- 
amic effects on the microcline crystals are as a rule manifest 
only in the development of cracks and of small mutual displace- 
ments of the fragments. 
In the egirine-lujavrite the felspars have been converted 
into analcime on a large scale. Only in a few specimens both 
microcline and albite have been found quite unaltered, in most 
cases they are partly replaced by analcime and sometimes the 
felspar-substance has entirely disappeared. Even in the latter 
ТА. L. Day and Е. T. ALLEN, The Isomorphism and Thermal Properties 
of the Feldspars. Carnegie Inst. Washington, Publ. No. 31 (1905). 
2 N. S. Kurnaxkow und $. Е. ZEMCUYNYI, Isomorphismus der Kalium- und 
Natriumverbindungen. Zeitschr. f. anorgan. Chemie, LII, р. 186 (1907). 
— Comp. also p. 149, above. 
XXX VIII. 11 
