Foliation and Sedimentation — Lairson. 177 
existence at great depths, under high pressure and temperatures 
is directly at variance with our knowledge or deductions as to 
the probable behavior of matter under such conditions. These 
rocks must therefore on Prof. W's. admission have crystal- 
lized from a magma; and as we have abundant evidence of 
small quantities of water in the rocks themselves, we are forced 
to recognize some sort of hydro-thermal fusion. The sooner 
the well defined line which exists in nature between rock meta- 
morphism and fusion is recognized by geologists, and the for- 
mer understood to stop where the latter begins, the better for 
the progress of investigation in Archaean geology. 
Another admission whereby Prof. W. places himself at one 
with myself is his statement that "we are at liberty to assume 
for portions of the gneisses any degree of fluidity which observed 
phenomena seem to indicate; and yet, for the great body of the 
gneisses recognize such a history as is indicated most plainly 
by the general tenor of the most accessible facts." 
The facts which prove the fluidity thus admitted are for the 
most part observed at the top of the Laurentian, and it is ad- 
mitted that the conditions inducing fusion were more intense in 
still deeper portions, although with increasing pressure the 
fluidity was perhaps less. At great depths the absence of 
brecciated fragments of the overlying schists, and of injected 
sheets and dikes renders the intrusive character of the gneiss 
less apparent; but the absolute identity of the rock with rocks 
known to be irruptive, and the unbroken continuity of the deep 
portions with the intrusive portions at the contact with the 
overlying schists, is sufficient proof that the admission which 
Prof. W. makes for portions of the mass is applicable to the 
whole. 
13. Prof. W. says : " Some of the difficulties experienced by 
geologists, especially German geologists and their followers, in 
admitting a former sedimentary condition of most gneisses and 
granites arises, probably, from too narrow a conception of geo- 
logical history." 
As to the difficulties alluded to I have, I think, made it suf- 
ficiently clear that I experience none in admitting the possibility 
of a former sedimentary condition for the Laurentian gneiss, 
and in one of my later papers I have advanced considerations 
in favor of probability of such a view. The only difficulty I 
