282 WwW. R. BROWNE. 
the strongly sodic residual magma, containing among other 
constituents alumina, silica, carbon dioxide and much water, 
attacked the already crystallized rock, or those portions 
susceptible toits influence. The felspar was albitized, and 
the olivine altered, while the augite was for some reason 
left untouched. This immunity of the augite, by the way, 
is a remarkably constant characteristic of many albitized 
basic rocks which have come under the author’s notice. 
Hven the albite became unstable under the conditions. 
obtaining, for it was subsequently attacked and replaced 
by zeolites. The residual mother liquor, its work of sub- 
stitution done, and enriched and modified by the assimila- 
tion of material from the olivine and felspar, eventually 
deposited its mineral constituents in order of increasing 
solubility in the interstices of the crystal network and in 
the steam-cavities. Thus as the temperature fell chlorite 
was deposited, then the soda-zeolites natrolite and analcite 
(in what order it is not clear), and lastly calcite. 
If, as seems possible, the amygdaloidal rock referred to 
above really represents the top portion of a flow, of which 
the calcite-rich basalt is a lower portion, then itseems as if 
the chlorite and the hydrous silicates were mostly deposited 
hearest the cooling surface and the calcium carbonate 
eventually concentrated at a lower level. 
It would thus appear that the solutions from which the 
calcite was deposited were essentially magmatic, and were 
really the same as those responsible for the chlorite, anal- 
cite and natrolite. This beingso, the question arises whether 
the calcite should be regarded strictly as primary or as: 
a result of the reactions referred to by Sederholm as 
‘‘deuteric.’’? Certainly, if the view as to its origin stated 
above is correct, the calcite has been produced as a result | 
of the alteration of primary minerals, but on the other hand 

1 Bulle Comme Geolominiande: Ne smene: 

