274 Hie Ariiericnn Geoloyint. Novcmbor, l.s95 
purfaee flows coteiuporavy with the sedimentation, wholly 
analagoiis to those of the Keweenawan. 
Whether these horizontal sandstones are involved with the 
tilted sandstones which form the southern extremity of cape 
Mamainse, at the eastern end of lake Superior, is ditiicult to 
ascertain from the description of Mr. Thomas Macfarlane.* 
That there are "horizontal sandstones" further south, which 
extend to Sault Ste. Marie, is generally admitted. 
There is ])ut one point further to be mentioned going to 
show" the later date of these Black Bay traps. Without in- 
cluding tlie peculiar dips and alternations of the sandstone 
beds at Mamainse, it cannot be questioned that the "horizon- 
tal sandstones" have been tilted locally since they were depos- 
ited. Such violent rupturing and bending as Sweet and 
Chamberlin and Irving describe and illustrate, the former in 
Douglass county, Wisconsin, and the latter along the south- 
eastern side of Keweenaw point, imply profound movements 
in the deeper seated portions of the rocky crust. It is reason- 
able to suppose, as Chamberlin and Irving have, that move- 
ments once begun along a line of weakness would be liable to 
recur there at later dates. Since they have recurred at later 
dates it may be inferred that their origination and recurrence 
have a common cause. Their origination was intimately con- 
nected wnth the fractures that marked the growth of the Lake 
Superior synclinal, and the outpouring of trap rocks. Their 
recurrence, therefore, must have had the same deep seated 
connection with that movement. In other words, the fractures 
and thrusts which are seen in the horizontal sandstones on the 
south side of the lake, not accompanied by trap outtlows so 
far as known, may have been accompanied by such phenom- 
ena on the north side, since on both sides of the great basin 
the rim would be likel}'^ to feel the effect of the settling at the 
center. 
In tine, although it may not be considered as altogether 
demonstrated that the Black Bay sandstones are no part of 
the Keweenawan proper, there is so much evidence tending 
that way that for the purposes of geological correlation the 
rational observer is compelled to accept it as probable, and to 
construct his taxonomy on that evidence as the most likely 
foun chit ion. 
*Ge()l()f?icRl Survey of Canada, 1866. 
