THE AGATE BAY BEDS. 291 
feet—were seen at a number of points, and it is quite possible that greater 
ones exist, though hardly such as could affect very greatly the estimate 
given for the total thickness of the group. 
Some peculiar appearances noted in the massive rocks in the upper 
part of the Agate Bay Group deserve further attention. At several points 
east of the mouth of Encampment River, bright-red bands an inch or two 
in width were noticed standing out on weathered surfaces. The bands are 
serpentine, making all sorts of irregular curls, and intersecting one another 
without any system. To the naked eye the bands and inclosing rock 
appear different only in color, even this difference being much less notice- 
able on a fresh surface. A thin section of one of these bands with some 
of the adhering wall rock, from the shore of the N. E. 4 of Sec. 12, T. 53, 
R. 10 W., shows plainly under the microscope that both band and inclosing 
rock are the same, save for the numerous red hematite particles and greater 
abundance of altered olivines in the former. This peculiar appearance is 
probably a flowage result. 
Another peculiar appearance is the resemblance to a bowlder-conglom- 
erate presented in a few places by some of the more massive layers. For 
instance, on the shore of the 8. E. 4 of Sec. 14, T. 54, R. 9 E., about two 
miles above the mouth of Split Rock River, the shore cliff is formed of a 
compact, purplish, fine-grained rock, which on a weathered surface presents 
the peculiar light and dark mottling so characteristic of the fine-grained 
olivine-diabases or melaphyrs. In other words, it is the usual massive rock 
of the Agate Bay Group. At one point, near the water’s edge, this very 
massive dense rock presented a marked stratiform appearance, though 
plainly grading on either side and upward into a rock without this structure. 
At the same time there appeared to be contained large, rounded, protruding 
bowlders. Close inspection showed these ball-like masses to be exactly the 
same as the rock inclosing them, into which they graded insensibly. The 
thin section of both rock and apparent bowlder proves to be a fine-grained, 
typical, luster-mottled melaphyr, with olivine and very abundant magnetite 
in the interspaces of the large augites. The structure is apparently referable 
to the spheroidal form so often taken on by basaltic rocks in cooling. 
Yet another, but quite different appearance, as of foreign masses con- 
