Origin of tlic ArcJican Igneous Rocks. — Winchcll. 305 
plasticity which must apply to the deeply buried sediments 
(Sixteenth Annual Report of the U. S. Geological SuA^ey, 
1897), and shows that by the c«-operation of aqueous and ig- 
neous agencies, simultaneously under great pressure, all rocks 
would be compelled to act in some measure the same as 
molten masses. Notwithstanding these suggestive links of 
connection between the igneous rocks and the cl?.stics which 
they penetrate, Van Hise does not propose, any more than 
Crosby and Fuller, that there is any genetic bond between the 
elastics and the granites. 
Although on several occasions there have been published 
in the reports of the Minnesota survey certain evidences of 
the transition of clastic rocks into crystalline rocks, such ^s 
gneiss, and granite-gneiss and finally into granite, there has 
not been until lately any careful investigation of the rocks 
themselves in their transitional petrographic characters. 
But one locality has been studied in this manner. The 
field observations need not be rehearsed, for the megascopic 
facts are published in detail in the reports of the survey. 
This locality is that about Kekequabic lake. Here is a granite 
that shows both the clastic and igneous characters, as exam- 
ined in the field. It is crystalline, massive and intrusive on 
the adjoining sediments, but grades off into fragmental rock, 
the gradation into fragmental rock being especially evident 
when the clastic rock was conglomeratic, the boulder forms 
of the coarse clastic still remaining. 
Without going any more fully into the field evidence, it will 
be interesting, perhaps, to note the petrographic transition. 
This area of granite is small, a circumstance that brings the 
whole series involved between the granite and the fragmentals 
within narrow limits and warrants greater confidence in draw- 
ing the important conclusion. It rises in the form of a small 
dome in the middle of the Lower Keewatin. The clastic strata 
adjacent consist of siliceous actinolitic schist, in general 
terms, but they vary in different ways. The hornblende ele- 
ment becomes coarser, and the rock assumes the character 
of a peculiar porphyry. At other times the hornblende is 
partly replaced by augite which is allied to segyrine, and in 
nearly all cases it can be seen to have been derived from 
augite by a uralitic alteration. This derivation is evinced chief- 
