SECTION NEAR THE MOUTH OF SPLIT ROCK RIVER. 
rock rises again to a height of over 150 feet. The inclusions of 
angular masses of the anorthite-rock in the gabbro indicate the 
more recent origin of the latter, and this conclusion is borne out by 
the thin section made from a specimen taken at its contact with 
the gabbro, in which the relatively fine gabbro surrounds the ends 
of the anorthite crystals, as the base of any porphyry does the por- 
phyritic crystals which lie imbedded in it. Since the strike is now 
trending somewhat more around to the northeast, and the dip at 
the same time flattening somewhat, this gabbro probably does not 
exceed in thickness Ssome....-............ Be erainisteteeiete sero tees 
IV. Ashbed-diabase and diabase-amygdaloid—The compact portions of this 
layer, which is a dark-gray or brownish-gray compact rock, macro- 
scopically like the rock of II, is largely exposed along the coast, 
in the N. E. 4 of Sec. 5, T. 54, R. 8 W., and See. 33, T. 55, R. 8 W. 
The overlying amygdaloid, which is seen at several points, has an 
aphanitic, dark-gray matrix, not unlike much of the compact rock 
below, while the amygdules are wholly of light pink laumontite 
lying in elongated, smooth-walled, closely crowded vesicles, aver- 
aging from ¢ to ? of an inch in greatest length. The amygdaloid 
is 26 feet thick, and the whole thickness of the layer probably not 
HIGIRS) UNE 5 .dc0n oboche pagb cbo UOC Hoe TE Gbcot oe aeoshoEsoarcomende 
V. Olivine-gabbro.—This gabbro is in sight, directly overlying the above de- 
scribed amygdaloid at several places along the shore of See. 33, T. 
55, R.8 W. It is a medium-grained to rather fine-grained, dark- 
gray to black rock, much like that of III. The thin section shows 
numerous rather fresh olivines; large diallagic augites, often includ- 
ing many plagioclases (labradorite); and titaniferous magnetite. 
This layer shows a strongly marked columnar structure at right 
angles to the bedding, and in places the columns are even cross- 
jointed, so as to show a rude ball-and-socket jointing. In places 
also weathering brings out distinctly a spheroidal structure. At 
a projecting point in the N. W. 4 of the N. E. 4 of See. 5, T. 54, 
kh. 8 W., this layer is crossed by a mass of coarse white anorthite- 
rock similar to that above described, and in the vicinity the gabbro 
holds numerous angular masses of the anorthite-rock. Thickness 
OP HAS TENG, QW Gnas oe coou cocoon og eoobecocoEde We cobra teistee See 
VI. Red quartziferous porphyry.—The rock of this layer is to be seen at the 
point in the northern part of Sec. 33; T. 55, R.8 W. The thickness 
OP UNS JERE IEPA SOUS 66665 Sh cen noooGEcshon ocegus cosaco as acS HOS 
Total thickness of the section............-- EOOSUBS Seaaas 
303 
900 
100 
100 
100 
2, 600 
The granite-like rock forming the end of this point may also be part of 
the last layer, and faulted down into its present position, but from its 
