268 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
grained diabases with amygdaloids are not excluded—though they are rarely 
met with. No detrital material has been observed. In following the coast 
line eastward the beds of this group are crossed in ascending order between 
Split Rock and Baptism rivers, a distance of some 18 miles; and in descending 
order in the 28 miles below Grand Marais; besides which are also exposures 
of the same beds in the intervening country back of the lake shore. In 
its eastern extension this group does not exceed 4,000 to 5,000 feet in thick- 
ness, but to the west it must fully reach, if it does not exceed, 6,000 feet. 
VI. Tue Temperance River Grour.—This is a succession of very dis- 
distinctly and thinly bedded fine-grained -diabases and melaphyrs, with 
strongly developed amygdaloids, and several seams of detrital matter, in 
the shape of red shaly sandstone and conglomerate, one sandstone layer 
exceeding 200 feet in thickness. Towards the base of the group are some 
layers of dense ashbed-diabase and diabase-porphyrite. The rocks of this 
group form the coast line from a point two miles below Baptism River to 
Grand Marais, a distance of 50 miles. They are the highest rocks seen on 
the Minnesota coast, and have a thickness in sight of some 2,500 to 3,000 feet. 
In giving more detailed accounts of these several groups, it will be 
most convenient to take them up in ascending order, considering in each 
case first the more western exposures, and then the eastern extensions. 
The Saint Louis gabbros and porphyries—The rocks of this group form 
a bold range of hills, extending from Duluth in a 8. 46° W. direction, seven 
miles on the north side of the Saint Louis River. They have also been car- 
ried northward from Duluth to the Cloquet River, and up that stream nearly 
to township 55, a distance of over 25 miles; the belt, as a whole, having 
apparently at first a northeasterly, then a northerly, and again a north- 
easterly trend, where left on the upper Cloquet River. How wide the belt 
is remains quite uncertain, a broad area of country without exposures lying 
west and north of it; but, judging from the relative positions of the west- 
ernmost exposures of the gabbro, and the easternmost of the underlying 
slates in the neighborhood of Fond du Lac, the width cannot there exceed 
two miles, if it reaches that distance.1 Equally a matter of inference is the 
‘Directly north, or even northwest from Duluth, one can travel on gabbro and intersecting red 
rock for some miles, but this is because the belt here trends northward. 
