THE KEWEENAW FAULT. 205 
southern dip along the south side of the Keweenaw Range,’ but I have since 
convinced myself by examination that no southern dip exists. 
To explain the sudden break on the south side of the Keweenaw Range 
between the Keweenawan beds and the Eastern Sandstone, Foster and 
Whitney long since’ supposed this line to be one of fault, and the Eastern 
Sandstone to be the equivalent of that on the west side of the range, the two 
separated only by the faulting. The latter position I shall show subsequently 
to be untenable;’ and yet that some faulting has taken place on this line, even 
after the deposition of the sandstone, is proven plainly enough by the fact 
that at the contact the sandstones commonly rise in a remarkable manner, 
presenting for short distances from the junction high southern dips. On 
Béte Grise Bay these dips reach 50° at the contact, lessening to 40° and 
30° within 200 feet, and to horizontality within a mile or less, Farther 
west the dips at the contact lessen in amount, becoming scarcely perceptible 
at Portage Lake, beyond which to the west they again become high. These 
phenomena are beautifully displayed at a number of points along the west 
branch of the Ontonagon, east of Lake Agogebic. 
These facts render it plain enough that some faulting took place on 
this line after the deposition of the sandstone, but the main faulting, I con- 
ceive, took place before. By this fault the Keweenaw Range escarpment 
and the valley south of it were first made, the width of the valley depend- 
ing on the amount of throw of the fault, which was thus greatest to the 
eastward. Subsequently the newer sandstone was deposited in this valley, 
and, after its deposition, a comparatively insignificant amount of faulting 
took place on the same line. On this view the South Range beds are 
the basal beds of the series, while the underlying basement of the interme- 
diate sandstone-filled valley is composed, in a measure, of the same beds as 
those forming the Keweenaw Range. 
1 Op. cit., pp. 65-66, 20p. cit., p. 68. 3Chap. VII. 
