NOTES. 435 
the basic rocks, having less than 48 per cent. silica. Of course the presence of strongly- 
marked amygdaloids and of intervening red shaly seams proves that these diabases 
succeeded each other regularly as flows at the then-existing surface, and that the last 
of them was succeeded in turn by the flow of the quartz-porphyry which makes up the 
mass of the Palisades. 
(3.) The occurrence of flows of intermediate acidity immediately overlying acid flows.— 
The porphyry of the Palisades just alluded to, or another flow closely like it, at the 
mouth of Baptism River, passes under a series of beds seen in a single cliff, in which 
the succession is as follows, beginning below: (1) brown, aphanitie diabase-porphyrite, 
with 52.5 per cent. of silica, thickness not measured, but under fifty feet; (2) black 
olivine-diabase, with crowning amygdaloid, and containing 50.76 per cent. of silica; and 
(3) brown diabase-porphyrite, with 57.87 per cent. of silica, and also furnished with a 
crowning amygdaloid. Thus, overlying a quartz-porphyry, we have im order a sub- 
basic, a basic, and an intermediate flow. 
(4.) The occurrence of flows of intermediate acidity overlying porphyry-conglomer- 
ates.—Intermediate flows are of course often met with at horizons in the series higher 
than occupied by beds of conglomerate. In the ease of the inner trap belt of the Por- 
cupine Mountains (pp. 214-217) a diabase-porphyrite, with 60 per cent. of silica, very 
closely overlies a porphyry-conglomerate, a small thickness of basic flows separating 
the two. 
(5). The occurrence of flows of intermediate acidity immediately superposed upon basic 
jlows.—A number of occurrences of this kind are to be met with among the Agate Bay 
and Lester River beds of the Minnesota coast (pp. 267, 279-294), but the only case in 
which the silica contents of the adjoining rocks have been determined is that of the 
cliff side one mile below the mouth of Baptism River, cited in the last paragraph, in 
which case an olivine-diabase, with 50 per cent. of silica, is overlain by a diabase-porphy- 
vite with 58 per cent. of silica, both rocks being plainly surface flows, since both are 
furnished with well-developed amygdaloids. 
(6.) The intersection of basic by acid rocks.—Coarse olivine-gabbro is intersected by 
granite in a number of places in the Bad River region of Wisconsin (Geol. of Wis., 
III, pp. 168, 183-193; this vol., p. 125). The coarse orthoclase-bearing gabbro of Da- 
luth (49 per cent. silica) is intersected by granitic and other acid porphyries (pp. 270- 
272). Granite-like rocks, apparently intersecting basic flows, occur at several points 
on the Minnesota coast (pp. 303, 305, 310, 329). On the Bohemian Mountain, on the 
north side of Lac La Belle, Keweenaw Point, red granitic porphyry apparently inter- 
sects a melaphyr (p. 184). 
(7.) The occurrence of basic flows overlying acid rocks.—The quartziferous porphyry 
of Baptism River, already several times cited, is closely overlain by a basic flow, and a 
number of other instances are to be met with on the Minnesota coast. In the region of 
the Ontonagon River and the Porcupine Mountains (pp. 206-225), and again in the Bad 
River region of Wisconsin (Geol. of Wis., pp. 195-198, and Atlas, Plate XXII) are sim- 
ilar occurrences. 
(8.) The occurrence of basic flows overlying those of intermediate acidity A number 
of cases of this occur among the Agate Bay beds of the Minnesota coast (pp. 284-294), 
and the same thing is met with in the inner trap belt of the Porcupine Mountains, as 
already described. 
