Editorial Comment. 
333 
appears when young as a straight, conical shell, but after its 
attachment to Platycrinus assumes a very different aspect. 
As growth proceeds the posterior side becomes relatively 
shorter, the apex slightly curved backward, and the entire 
shell has frequently a tendency toward a strongly arcuate 
form. 
In comparison therefore with a representative example of 
Platyceras equilaterum those shells resting on flat crinoidal 
vaults are very much depressed, the aperture proportionally 
broader, and the spire more closely coiled ; those shells at- 
tached laterally to crinoids have a tendency to become more 
conical, the aperture relatively smaller, the spire entirely free 
from body whorl, and the apex extended often to a consider- 
able distance beyond the posterior margin of the aperture. 
EDITORIAL COMMENT. 
UNCONFORMITY AT THE FALLS OF THE MONTMORENCI. 
There seems to be a question of fact at issue respecting the 
stratigraphic relations of the different rocks at the falls of the 
Montmorenci, a few miles below Quebec. In the August 
(1888) No. of the Geologist, is reprinted an article from the 
A-merican Magazine of Nov. 1847 by Dr. E. Emmons, giving 
a description of these falls and the geology of the immediate 
vicinity. The illustration there alluded to was not repro- 
duced. In order to throw some light on this description by 
Emmons the following illustration of the falls is reproduced 
from his ''Manual of Geology," published in 1860, which corres- 
ponds closely with the description referred to. 
■Unconformity of the Lower Silurian with the Gneiss at Montmoroncy, Canada East. 
t, d, c, b. Lower Silurian, o. Gneiss. /. Bl«ok S'nto. 
It is very evident, from a careful reading of this paper, that 
Dr. Emmons, at the time it was written, which must have been 
