148 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
right angles to the dip of the mass, are here just as in the Palisades. The 
same fine banding also appears in places, but is warped up and down, so 
as to change from horizontal to vertical within short distances. This rock 
is traced along the coast for about three-fourths of a mile, when it again 
disappears underneath another series of diabases and amygdaloids, inter- 
leaved with which are thin seams of red shale, and one bed of curiously 
intermingled shale and amygdaloid, precisely resembling the Ashbed of 
Keweenaw Point. Still three-fourths of a mile beyond, to the northeast, 
these diabases are overlaid by a pebble conglomerate, in which the matrix 
is red shale and the pebbles rolled fragments of diabase and amygdaloid. 
The occurrence of the porphyry of the Palisades and of Baptism 
River has thus been given at some length in this connection because the 
relations of the basic and acid rocks are here so unmistakably plain, and 
because upon these relations rest important conclusions. There can be no 
doubt whatever that we have here, between two sets of perfectly and 
typically developed diabases and amygdaloids, those on the upper side car- 
rying the customary seams of red shale, a true layer of quartziferous por- 
phyry several hundred feet in thickness, while in the previous chapter it 
has been shown that this porphyry is as truly an eruptive rock as the asso- 
ciated basic kinds, presenting as it does all characters of an eruptive por- 
phyry, viz: a base made up of imperfectly individualized or incompletely 
devitrified material, doubly terminated quartzes with inclusions of the base 
and of unmistakable glass, and flowage lines. 
Although these rocks show at numbers of other points on the North 
Shore, the relations of the porphyry to the diabase flows are not always to 
be so well made out at first sight as at the Palisades. Often the porphyry 
exposures occur separated from any exposures of other rocks by long peb- 
ble beaches. Again they form merely projecting points, or restricted areas 
between dark-colored rocks, apparently owing their preservation to a 
sudden bowing down of the strata, so that they represent subordinate 
synclinals impressed upon the general lakeward dip. In other cases they 
come into abrupt and vertical contact with dark-colored diabases, and form 
masses which have been faulted into their present positions. Wherever these 
less plain occurrences have been closely studied, however, it has become 
