162 FORMATIONS OF THE INTERIOR 
some of these have much the appearance of impressions of organic bodies, but they 
are so indistinct that no definite structure could be observed with a common 
magnifier. 
From thirteen to fifteen miles from the head of the rapids, a dip was observed of 
the strata of red sandstone, in an east-southeast direction, at an angle of about 13°. 
It was only on the river that the sandstone could be discovered in place. Nothing 
but sand, gravel, and drift, could be found exposed on any of the ridges which I had 
an opportunity of examining, even to the height of one hundred or one hundred 
and twenty feet. 
All the rapids above the mouth of the Namekagon seemed to be formed by ledges 
of the same red sandstone, varying from its usual appearance to that of a schistose 
argillaceous rock. 
After passing the Namekagon a mile or two, there are no more rapids of any 
consequence, until after passing Yellow River. 
The ridge over which the portage leads from the St. Croix to Yellow Lake, I 
found to be from eighty to a hundred feet high. Its direction is east-northeast 
and west-southwest, which, indeed, is the course of most of the ridges on the St. 
Croix, they being parallel with the trap ranges of the upper part of the Brulé. No 
trap can be seen here in place, nor, indeed, thus far on our descent down the St. 
Croix, probably on account of the thickness and extensive range of the drift 
deposits. The size and number of the trap boulders on the Rapids, and lining the 
shores, induce the belief that they are not far removed from the range of intrusive 
rocks from which they have been derived, and which probably constitutes the nucleus 
of many of the ridges of the Upper St. Croix. 
About four miles below the Yellow Lake portage trail, a small stream flows into 
the St. Croix from the northwest, the Eninandigo River (?) of Nicollet, and two or 
three miles further, Turtle River enters from the southeast (Kayesikang or Shell 
River of Nicollet (?). A mile or two below this are banks of sand and gravel, similar 
to those described on the Lower Chippewa, but of a redder colour, and from twenty 
to seventy-five feet high. 
There are many fine Unios in the St. Croix; most of the species seem to be the 
same as those found in the streams of the Western States, though they have a 
slightly modified outline of form. Among them I noticed U. undulatus, siliquoides, 
crassus, cuneatus, mytiloides, gibbosus, and alatus. These fresh-water mollusca 
seem to be more abundant on the St. Croix than on the Chippewa, Bad River, or 
the Brulé. A few were observed even as high up as the outlet of the Upper Lake 
St. Croix. 
This part of the St. Croix is about sixty yards wide. It flows smoothly along, 
without rapids or ripples; the bottom is sandy, and boulders are less frequent 
along the shore. 
The adjacent ridges seem composed chiefly of sand and drift, and are clothed 
with “pine openings.” Four or five miles above the mouth of Kettle River is a 
beautiful stretch of bottom land, with picturesque groves of white oak and aspen, 
above the reach of high water. The soil, however, is light and sandy. 
Just below this, a few boulders appear again in the bed of the stream, and rapids, 
