1903 - 4 .] Mr J. G. Goodchild on Intrusive Bocks. 
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tact with the rock invaded. Hence the magma was enabled to 
advance along the joints and other divisional planes of the country 
rock. Every stage of the process can be traced, from the first 
insinuation of a thread, or a knife edge, of granite, through the 
later stages of development, where the advancing mass has widened 
out, and has begun to form a thick wedge, up to the point where 
it has eaten its way so far into the adjoining rock that the portion 
attacked has become surrounded by the fluid magma, and thus 
ready to float away as an isolated mass into what one may term 
the trunk stream. (Here, perhaps, it may be as well to repeat 
the remark that I do not entertain the belief that the fluid granite 
is simply so much quartzite or greywacke in a different state from 
what it was at first. Granite cannot be made simply out of 
greywacke, much less out of quartzites, for there are several im- 
portant constituents present in the eruptive rock which are absent 
from the other.) But the advance of the veins of granite into 
the schists, the enlargement, ramification, and coalescence of 
contiguous veins, carried on until the two are closely spliced into 
one, can be seen in every stage of progress. Whatever may have 
been the particular solvent, its mode of operation is sufficiently 
evident from a study of the various intermediate stages in the 
process of, what may be termed, the mastication and assimilation 
of which records have been left. The process has clearly been 
of a physico-chemical nature, and one in which the continual sub- 
division of the rock undergoing attack has been effected by the 
erosive action of the peripheral parts of the magma. Each stage 
in the process of comminution has led to an increase of the area 
being exposed to attack, and has led, finally, to the complete solu- 
tion of the fragments. I have long regarded the basic inclusions so 
often found in plutonic masses as incompletely assimilated portions 
of the country rock. This view, I am glad to notice, is now 
being adopted by many of the rising generation of field geologists. 
Some reference has already been made to the different mode 
of attack followed by the more basic as compared with the more 
acid magmas which, by the way, I should like to refer to hence- 
forth under the respective terms soda magma and potash magma. 
The evidence appears to suggest that the soda magmas in general 
acted with more corrosive effects at the extremities of their masses, 
