Geology of the St. Croix Dalles. — Berkey. 35."? 
The first or 905-foot terrace. 
The second or 810-foot terrace. 
The third or 780-foot terrace. 
The fourth or 750-foot terrace. 
The fifth or 725-foot terrace. 
Traces of all five are found north of the villages along the 
river. The sand covered flat in Sec. 2, T. 34 N., R. 19 W., is 
a terrace flat. 
The 905-foot tei'race belongs to the period of ice retreat and is dis- 
cussed under Glacial Geology. 
The 810 foot terrace is most prominently marked in the village of St. 
Croix Falls, where it is coincident with the main business street and 
forms a striking bench extending for more than half a mile along the 
river. This terrace marks the stage of the river corresponding to tht^ 
development of the abandoned channel in Sec. 36, T. 34 N., R. 19 W., 
and doubtless indicates a check in the erosion of the river gorge. The 
river was held at this level until an entirely new channel had been de- 
veloped toward the west through the sandstones and shales. These 
formations permitted a more rapid erosion than the volcanic rocks 
which formed the floor of the abandoned river bed. 
The 780-foot terrace is prominently marked northward from St. Croix 
Falls along the wagon road for a distance of two miles. The arrest in 
erosion causing the terrace comes from the two barriers or dams of dia 
base, one at the elbow of the present Dalles and the other a mile north 
at the present St. Croix falls. At the time of this terrace building the 
river made use of an abandoned channel plainly marked through a part 
of the northeast M Sec. 25, T. 31 N., R. 19 W., in the village of Taylor's 
Falls, now occupied by the St. P. & D. freight depot and tracks. The 
northernmost barrier was so readily destroyed that further erosion of 
this channel was checked, although a portion of the river used this side 
until it had cut below the 760-foot contour. 
The 750-foot terrace is easily traced on both sides of the river for a 
mile above the Dalles. It is the most pronounced of all and mark.s 
probably three events: 1st, it awaited the erosion of the narrow gorge 
from the elbow to the toll bridge, which made it possible for outflow at 
a lower level: 2d, it marked the period of most prominent pot hole ero- 
sion; 3d, it seems reasonable to conclude that it marked at least the be- 
ginning stage of a very considerable decrease in the amount of water 
discharged by the St. Croix. 
The 725 foot bench on the Wisconsin side marks a stage claiming a 
place among the group of terraces. It is developed at no place so well 
as immediately above the toll bridge. And it marks the last serious 
check in the erosion of the present very narrow channel through the 
Dalles. 
On the Minnesota side of the river opposite Hudson, Wis.. 
