;55() 21ie American Geologist. December, imit 
loiiiid also in Sec. HG, occupying the rocky bed of the oltl 
channel used at the time of the formation of the 810- foot ter- 
race. At this same time the erosion at the foot of the rapids 
I'ollowing what now constitutes u rock-bound ravine or valley 
through the northern part of Sec. 1, T. 33 N., R. 19 W., was 
sufficient to form the basin now occupied by Folsom lake. The 
river lakes lying in sections 10, 11, 14 and 15 are probably of 
more recent origin, but date back at least to a time when the 
volume of water in the St. Croix river was much greater 
and the channel at this point mucli wider than at present. 
The igneous rocks, reaching the river at this place, intro- 
duced an obstacle to further erosion of the eastern portion of 
the channel, while the subsequent accumulation of river sand 
has barred off this chain of lakes. 
Springs. The number of springs,* especially along the riv- 
er, is very great. There are a few also farther back at either 
side of the river at a greater elevation. Those issuing at a 
low elevation along the river may be called river blulf springs ; 
those issuing from the drift at a comparatively high eleva- 
tion may in contrast be called drift springs. 
The river blutf springs are almost without exception con- 
lined to the upper Dresbach shales and sandstones, below 
the 800-foot contour line. They owe their existence to the 
presence of the river gorge, which makes it possible for the 
saturated glacial sands and Cambrian sandstones to dis- 
charge the surplus water at the level of the more impervious 
shales and igneous outcrops. Locally, these sedimentaries are 
completely covered by recent debris of the river blutfs, but 
their true relations can scarcely be mistaken. At such points 
the springs seemingly issue from the glacial drift, but the 
drift in no case causes the flow. These springs are found 
continuous!}^ along the bluffs on both sides of the river. The 
most remarkable ones issue from the wooded slope lying be- 
tween the 750-foot and the 810-foot terraces on the Wisconsin 
side of the St. Croix river in the village of St. Croix Falls. 
One also occurs in 'I'aylor's Falls village at the same level. To 
these should be added the Franconia springs, which are the 
chief supply of Lawrence creek. 
The glacial drift springs are all above the 800- foot contour 
*Geology of Wisconsin., vol. Ill, 1880, p. 374. 
