Review of Recent Geological Litetature. 123 
rocks, which is probably one of the most complete and reliable ever 
made, as it depends on positive data — even allowing for mistakes made 
by the foremen, and for accidents that sometimes confuse and impair 
deep well records. There were made fourteen drill-holes, the deepest 
being 1,038 feet. These are so distributed that, by comparing their 
records, allowing for their overlapping and for faults, they develop a 
total thickness of strata amoimting to 6,400 feet, of which, at the bot- 
tom, about 250 feet consist of red felsyte. They consist of lavas and 
amygdaloids, with conglomerates. 
The discussion of this section, and the extension of its significance 
so as to cover the whole of Isle Royale, coupled with some examina- 
tion further east, constitutes the larger part of Dr. Lane's report. 
He adds, however, an important chapter on diabase dikes on the 
south side of lake Superior, which cut there the rocks of the iron-bearing 
series, and which are considered the equivalents of the intrusive "Lo- 
gan sills" of the Animikie, described by Lawson, thus representing on 
the south shore the same relations to the rocks of Keweenaw point 
as the sills of the Animikie bear to the flows of Isle Royale. 
The scientific work of Dr. Lane is marked by his well-known 
thoroughness and penetrativeness. This is exhibited not only in his 
cautious treatment of the question of the succession of strata in the 
drill-holes studied, but also in his discussion of "the grain of rocks," 
and in his petrographic investigations. We can only briefly note some 
of the most important scientific conclusions of Dr. Lane's report, viz.: 
1. He is disposed to approve Irving's rather than Lawson's esti- 
mate of the thickness of the Keweenawan of the north shore of lake 
Superior, and makes a suggestive attempt to correlate the parts of the 
Isle Royale section with the principal members of Irving's section 
between Duluth and Pigeon point. 
2. He allows for several faults in the Isle Royale section, some 
existing with tolerable certainty and others having a rather "retiring 
disposition," and being, perhaps, assumed rather than proved. 
3. Overlying the section of rocks penetrated by the drills is a 
great thickness of conglomerate and red sandstone amounting to 
2,600 feet, these occupjang the southwest part of the island. This may 
contain also later lava flows, but no drill-hole has penetrated it. 
4. There is no "proper gabbro" on Isle Royale, at least none has 
been discovered. 
5. The rock locally known as "The greenstone" on Isle Royale is 
a coarse ophitic diabase, extending the whole length of the island 
and constituting its highest parts. This is a gigantic surface flow, 
233 feet thick, and is supposed to correspond with a similar member 
of the Keweenaw Point section which has a thickness of 1.193 feet, 
and to the Beaver Bay diabase of Minnesota. 
6. Under the head "grain of rocks" some of the common notions 
as to rate of cooling being dependent on the bulk of the mass and the 
relative .size of the grain being a result of slow or quick cooling are 
