Editorial Comment. 51 
viously existing sand beds, by the violent currents set in motion 
at tbe time of the trappean intrusions. (4). The inclin- 
ation southeastxvard in the eastern sandstone at the junction 
with the traps, and that to the noi-thxvestward of the sandstones 
and conglomerates of the copper-bearing series, are due to the 
intruding trap. This view is discarded because the contempor- 
aneous, or lava-flow origin of the traps has been repeatedly and 
abundantly demonstrated. 
The Foster and Whitney vlext\ as summarized, contains six 
propositions, (i). The eastern sandstones and the Kewee- 
naw detrital rocks are one and the same formation. (2). 
The associated igneous rocks are of two classes: (a) Traps 
that are interleaved with the detrital rocks, of lava-flow 
origin, (b) the traps of the Bohemian range, which are held 
to not be bedded but massive and intrusive, and of later origin 
than the detrital rocks and their interbcdded traps. (3). This 
later eruption of trap was the cause of the tilting of the bedded 
traps on the north side toward the northwest, and the sandstones 
on the southerly side toward the southeast, and of the produc- 
tion of "jasper" masses by a change of the detrital rocks. (4) 
The conglomerates of the trappean series are mainly of igneous 
origin, the rounding of the pebbles being due, not to water 
action, but to friction of the elevated rock against the walls of 
the fissures. To the production df these conglomerates, by 
eruptive agencies is to be attributed the immensely increased 
thickness of the detrital portions of the formation in the region 
of Keweenaw point. (5). The various bedded eruptives of 
Keweenaw point reached the surface through a series of fissures 
along the course of the point. (6). The massive trap of the 
Bohemian range was extruded through an immense fissure which 
extended as far west as Gogebic lake; running along the south- 
ern edge of what is now the trappean formation; but along 
its western extension this fissure was not accompanied by any 
igneous outflow, thus allowing the sandstones of the northwest to 
come immediately against the eastern sandstones. 
The first of these propositions the authors think is not sus- 
tained by results of microscopic examinations they have made of 
thin sections of these two sandstones. They find the eastern 
sandstone always much more quartzose and the grains much 
