190 AGE OF THE RED SANDSTONES 
trap, in place. So, also, on Snake and Kettle Rivers, ascending to the northwest, 
the change is gradual, from the buff and white quartzose sandstones prevailing on 
the St. Croix, below the mouth of Snake, to the reddish-brown, argillaceous, ferru- 
ginous variety. 
Now, it is very certain, that (if they still occupy, undisturbed, their original 
position) these red sandstones, so closely resembling, in aspect and connexion, the 
formation of Lake Superior, must rise from beneath the quartzose sandstone of 
F. 1, and must constitute, in fact, one of the inferior beds of that formation. And 
so of the red sandstones in further ascending the St. Croix. As a general rule, 
they retain their red tint, their argillaceous, ferruginous character, and their south- 
easterly dip, as far as any rocks can be traced, in place, up that stream, and until 
they disappear, under the drift, some ten miles below Upper St. Croix Lake, which 
is the source of the river. 
Here, it is true, an interval of some width occurs. From the point where these 
rocks are lost, under drift, on the Upper St. Croix, across to where other red sand- 
stones, similar in appearance, in their associated rocks and in their dip, are found 
in place on the Bois Brulé of Lake Superior, it is, in a northerly direction, about 
twenty-three miles; the intervening space being a region of heavy drift and 
erratics, in which no rocks whatever can be reached, in place. 
Here is a close approximation to proof, by superposition, that the red sandstones 
of Lake Superior underlie the Lingula and Orbicula beds of the Upper Mississippi 
Valley, represented on Tab. 1, B. The proof would be complete, if we could be 
assured, that the sandstones of the Upper St. Croix, and of Snake and Kettle 
Rivers, with their general southeasterly dip, have preserved the inclination of their 
original deposition ; and, further, that in the drift-covered interval of twenty-three 
miles, now devoid of visible rocks, there is continuity of strata and persistence of 
general dip. 
It is an imaginable case, however, and one which may be advanced by those 
who set down the sandstones of Lake Superior as of Upper Silurian or Post-Silurian 
date, that, at some remote distance of time, there might have existed two indepen- 
dent geological basins, of which the margins came together in the vicinity of the 
confluence of Snake River and the St. Croix; that, in the southern of these two 
basins, stretching down the Mississippi Valley, there might have been deposited 
sandstone of Lower Silurian date; while, in the northern basin, at a subsequent 
era, the red sandstone, with its subordinate slates and conglomerates, might have 
supervened, say at the Old Red or New Red Period. 
P -— 
re ie 
= eee 
= = g 
ee (gee Pas s 
: s 
— um oe ness ~ 8 g 
a coseg g Fo os a 
7) aets one ies os 
Resa SEs pos © 
ct SACK Sor a “s 
; d — ~ I od 
a Light-coloured quartzose sandstone. = Fo | tone. « 
jon ak ee 
ne = Ss 
A NIE [SSS 
THEORETICAL SECTION OF TWO ANCIENT BASINS, ONE OF QUARTZOSE SANDSTONE, THE OTHER OF RED ARGILLACEOUS 
SANDSTONE, IN THEIR ORIGINAL UNDISTURBED CONDITION. 
