ROCKS OF THE UPPER ST. CROIX. 249 
In the S. W. 4 of Sec. 22 (T. 43, R. 14 W.) there is an outcrop of a fine-grained, 
hard, reddish-brown, crystalline rock, probably a diabase. It forms the nucleus of a 
hill. 
In the 8. E. 4 of the N. W. 4 of Sec. 28 there is a small uncovered area of typical 
melaphyr, which probably belonged to the same stratum as those situated in Sees. 
14 and 27, T. 44, RK. 13 W., as already stated. From this point, for a distance of about 
30 miles down the Saint Croix, no exhibitions of rock in place of any kind are known 
to exist. 
The following is a description of the same district by Mr. E. T. Sweet:! 
In the banks and channel of Moose river, on Sec. 2, T. 44, R. 13 W., there are 
low ledges of melaphyrs and diabases, dipping 18° 8. 35° E. These are conformably 
overlaid by fine conglomerates and coarse sandstones. The pebbles of the con- 
glomerate have nearly all been directly derived from the underlying crystalline rocks, 
and are held together by a coarse, red, sandy matrix. None of the very coarse or 
bowlder conglomerates noticed on the northward-dipping belt, in Ashland county, and 
on the Saint Croix river, were observed here. In following Moose river southward, 
towards its mouth, several small exposures of the fine conglomerate were seen, but it 
apparently has no great thickness, for it soon grades into coarse, reddish sandstone, 
and that finally, after reaching the Saint Croix, into quite fine-grained, red sandstone, 
often somewhat argillaceous. 
The most northern exposure of this sandstone on the Saint Croix, is at the head 
of a small lake about a mile above the mouth of Moose river. The outcrop is in the 
east bank. The layers are hard and thin, and contain many red argillaceous spots. 
Indurated smooth slabs come out readily. A few of the layers are finely ripple- 
marked. The strike is N. 53° E. and the dip 1498S. This place is a short distance 
below Chase’s dam, on Sec. 36, T. 44, R. 13 W. For five miles along the Saint Croix 
below Moose river, a few small exposures only are seen. On Sec. 8, T. 43, R. 13 W. 
the sandstone is exposed in the banks five or six feet high. At the first considerable 
exposure, the rock is fine grained, very thin bedded, and argillaceous. Circular red- 
dish and bluish spots of indurated clay are of frequent occurrence in the layers. The 
strike is N. 55° E. and the dip 13° S. There are two well-marked systems of joints; 
one trending N. 28° W., and the other N. 55° KE. <A short distance below here, there 
is a somewhat larger exposure, showing a strike of N. 53° E., and dip of 149 S. Below 
this, for a distance of ten or twelve miles, tilted sandstones often form the bed of the 
stream, although they are seldom seen in the banks. In the banks of Rocky Run on 
Sec. 9, T. 42, R. 14 W., a half mile from the Saint Croix, the sandstones are again 
largely exposed. In the banks and channel of the Saint Croix, at Pine Rapids, a 
quarter of a mile below Sawyer’s old dam, on the S. W. 4 of Sec. 16, T. 42, R. 16 W., 
is the most southerly outcrop of the southward-dipping sandstone observed. The 
rock is very similar to that above described. The strike is N.52° E. and the dip 16° 8. 
These descriptions, with the map I have constructed from them (Plate 
XXYV), will serve to show plainly enough that we have in this region some 
1Geology of Wisconsin, Vol. III, p. 349. 
