OCCURRENCE OF CALCITE 1N A BASALT. 283 
its crystallization began when the rock was not more than 
86 per cent. crystallized, and again, it has been shown,» 
experimentally and otherwise, that in some igneous rocks, 
certain of the minerals of later crystallization have resulted 
from interaction between the magma and minerals already 
crystallized from it, which for some reason have become 
unstable.* It would probably be difficult to define the 
limits separating primary and deuteric crystallization, as 
the two stages appear to grade into one another. How- 
ever, in the present case, in view of the fact that the calcite 
forms such a large proportion of the rock, and that it is 
essentially not a replacement but an interstitial filling, 
there is surely justification for regarding it as primary. 
It is interesting to note in passing that Holmes, in inves- 
tigating the lavas of Mozambique, came to the conclusion, 
from the nature of their vesicle-fillings, that the alkaline 
basalts must have been crystallized from a magma con- 
taining much carbon dioxide,’ a state of affairs which must 
be postulated in the present rock-mass, which has very 
evidently alkaline affinities, and indeed has much in com- 
mon with the spilites. 
Vesicle-fillings of calcite have been noted by the author 
in other rocks which have been affected by wandering 
magmatic solutions. At the village of Gosforth, about 
eight miles north-west of West Maitland, there is a flow of 
basalt, just a little distance stratigraphically above the 
Lochinvar shales: in its upper parts it is albitized and 
interstitial natrolite is found, but another and lower phase 
of the flow contains unaltered basic plagioclase, and its 
vesicles are filled with calcite. 

' See, for example, Bowen, Journ. Geol., Vol. 23, 1915, supplement. p. 
39, etc.; Duparc and Hornung, Comptes Rendus, Vol. 139, 1904, p. 223; 
Thomson, Geol. Surv. of W. Aust., Bull. 33, 1909, p. 134. 
7 A. Holmes, Q.J.G.S., Vol. 72, 1916, p. 253. 
