THE LAKE SUPERIOR SYNCLINAL. 413 
beneath the newer formations in the vicinity of the Sault Saint Marie; that 
the western extension passes on to the south shore of Lake Superior with 
_a course curving more and more to the southwest until, at the termination 
in the Saint Croix Valley—and therefore without the present hydrographic 
basin of Lake Superior—it becomes nearly due south, the exact termina- 
tion here again being buried beneath the newer horizontal Cambrian for- 
mations; and that, in the region of the Porcupine Mountains of Michigan, 
_and the Douglas County Copper Range of Wisconsin, there are minor folds 
superinduced upon the grand synclinal, accompanied in the former case at 
least, by further complications, due to faulting. 
The evidence upon which these conclusions are based is to be found in 
(1) the nearly constant dip inwards of the Keweenawan strata towards the 
middle of the basin; (2) in the frequently similar dip of the Huronian; (3) in 
the constant order of Upper Keweenawan, Lower Keweenawan, Huronian, 
and gneiss with granite and folded crystalline schists, met with on all sides on 
going from within the supposed trough outwards; and (4) in the parallelism 
between the courses of the Keweenawan belts of the North and South 
Shores, and of the shore line with these belts. 
The details of the evidence under the first three of these heads are 
given in Chapters VI and VI, and on the maps and sections of Plates I, 
XVII, XVIII, XXII, XXIII, XXVI, and XXVII, and need not therefore 
be repeated here. That under the fourth head, however, needs some fur- 
ther remarks. In the first place it is to be observed that the drawings, from 
which the accompanying maps of Lake Superior, Plates I and XXVIII, are 
reduced, are much more accurate than any previously made with geological 
data, being compiled directly from the maps of the United States Lake Sur- 
vey, from Captain Bayfield’s chart, and from the United States land-office 
plats; and that, consequently, correct ideas may be obtained from them as 
to the courses of the coast and other topographical lines, and of rock belts. 
Directly north of the east and west portion of Keweenaw Point, be- 
_tween Agate Harbor and Copper Harbor, with its east and west rock belts, 
dipping north, we find the east and west part of Isle Saint Ignace again made 
up of east and west rock belts, which now, however, dip to the south. West- 
ward from Agate Harbor and Eagle Harbor, on Keweenaw Point, the coast 
