338 
lujavritic structure does not imply the assumption that abso- 
lutely all parts of the magma must crystallize to a schistose 
rock, nor that the rock must always be fine-grained, as would 
be the case if the size of grains depended upon the chemical 
composition only. 
it will also be seen that the assumption of a solid and 
passive substratum is an important point in the interpretation 
of the schistose structure. At Ilimausak the presence of this 
kind of substratum cannot be proved by direct observations, 
but its presence may be inferred with great probability from 
the form of the upper surface of the lujavrite body which has 
been actually observed. On the other hand, it must be remem- 
bered that the simplest explanation of the passive substratum 
depends upon the assumption of an exceptionally low temper- 
ature of consolidation for the lujavritic magma, and we are, 
thus, referred back to the chemical composition of the magma 
as the ultimate cause of the peculiarities of the lujavritic 
structure. 
It might, therefore, be expected that lujavrites also at other 
localities would often show structures like those of the Ш- 
mausak lujavrite. Some other occurrences of lujavrite have 
already been described, but in these the analogy with the Ш- 
mausak rock is very striking. 
The most important lujavrites outside Greenland are those 
of Kola! and of the Transvaal”, and from both localities the small 
size of the crystal grains and the schistosity are mentioned as 
usual and characteristic features of the rock. A similar structure 
also characterizes the lujavrite of Ruma’. 
1 W. Ramsay, Das Nephelinsyenitgebiet auf der Halbinsel Kola Il. Fennia 
VERNON 221899. 
?Н. A. Brouwer, Oorsprong en Samenstelling der Transwaalsche Nephe- 
liensyeniten. s’Gravenhage 1910, р. 107. 
ЗА. Lacroix, Sur les facies de variation de certaines syénites néphéli- 
niques des iles de Los. Comptes rendus CXLII, 1906, p. 681. 
