192 AGE OF THE RED SANDSTONES 
between the heads of the Brulé and St. Croix, is but 120 feet; and though the eastern 
extension of the ridge in question, between the Manidowish and head-waters of 
Montreal River, reaches an elevation of about 1,150 feet, its entire elevation above 
the Lake level, where it separates the St. Croix and the Brulé, scarcely exceeds 650 
feet; and, as it extends westward, it sinks to less than 500, probably to 400 feet. 
To all this is to be added the highly important fact, substantiated by Dr. Nor- 
wood’s observations and my own, of the general prevalence throughout all the sand- 
stones (ferruginous, as well as light-coloured, of Wisconsin and Minnesota, whether 
west or south of Lake Superior,*) of a southeasterly dip,—a phenomenon wholly at 
variance with the supposition that a basin once existed, stretching, with a northern 
dip, from its southern margin on the Upper St. Croix; a phenomenon, in fact, 
which can be reasonably explained only by regarding the great Plutonic chain, 
which lies north of the Lake, and runs nearly parallel with its north shore, from 
northeast to southwest, as the main axis of dislocation, whence the sandstones in 
question stretch, with a long, gradual, southeasterly slope, not arrested, in its ge- 
neral inclination, by the low water-shed between the Lake and the Mississippi, but 
passing on, and reaching down the valley of that river, until it disappears beneath 
the Lower Magnesian Limestone of Southern Wisconsin. With this view coincides 
the fact, that the dip in question is considerably greater north of the Lake than 
south of it. From its south shore, across to the Mississippi Valley, the dip of the 
strata, when undisturbed by subordinate igneous intrusions, does not, probably, ave- 
rage more than six or seven degrees; and, at many localities, it approaches a level. 
I conceive, then, that the natural and reasonable inference, in ascending the St. 
Croix and meeting red sandstone beds, with a dip corresponding to that of the adja- 
cent white and buff sandstone, is, that the red sandstone in question is a lower 
member of F. 1, and that the white and buff layers do actually rest conformably 
upon it. 
This reasonable inference is further confirmed by the fact, that, on several locali- 
ties, on various other tributaries of the Upper Mississippi, phenomena somewhat 
similar to those noticed on the St. Croix have been observed. On the St. Peter’s, 
near its confluence with the Waraju ; on the Wisconsin, eight miles above its Dalles ; 
on the Barraboo, near Devil’s Lake; on the Cedar Branch of the Chippewa, near its 
head,—the lowest beds of sandstone, found usually in proximity to the low ranges 
* With the exception of the high, northern dip of the sandstone, at the mouth of Montreal River (see 
Colonel Whittlesey’s Section, No. 4, and also the wood-cut at the close of this chapter), tilted by a trap 
range, which cuts across that river, only a few hundred yards above its junction with the Lake, there has 
not been observed, on the southern shore, from Montreal River to Fond du Lac, a single bed of sandstone 
or its associated rocks, of which the dip, when it could be detected, was not southeasterly ; not one which 
dipped northerly towards the Lake; though many writers have assumed this latter to be the true state of 
the case, and have thence been led into sundry false conclusions, touching the formations of this region 
of country. 
On the several forks of Bad River (see Colonel Whittlesey’s Sections), on the Brulé, and other Wis- 
consin streams that empty into the Lake, there are, crossing them at certain points, trap intrusions, which 
tilt the strata, often at a high angle, to the north, for a limited distance; but as soon as their immediate 
influence ceases (which rarely reaches two or three miles, usually much less), the strata conform to their 
usual place of deposition, to the southeast. 
