364 21ie American Geologist. December, ibJiT 
line of section 5, T. HB N., R. 18 W. Tlie valley in its south- 
ern extension, includes the greater part of sections 7 and 18, 
T. 33 N, R. 18 W., and sections 13, 14, 23 and 24 of T. 33 N., 
R, 19 W., and is continued beyond the bounds of the St. Croix 
Dalles area. Western material is found abundantly strewn 
among the pebbles around Dresser .Junction. The greater por- 
tion of the plain is composed of modified drift. This valley 
seems to mark the farthest advance of the western ice lobe. 
And, as the ice melted back, it became the course of a river 
which carried away the later glacial floods. AH parts of this 
valley near the moraine are deeply covered with coarse sand. 
Farther away from the morainic source of supply the more 
level stretches of tlie plain have comparatively good soil. A 
second tributary to the plain stretches through section 18 and 
develops into a deep, sandy ravine leading into section 4, 
toward Poplar lake, which nestles among the morainic hills. 
Except for the igneous rocks eneountex'ed in the former chan- 
nel, this old drainage course seems to be as important as that, 
and has no doubt been in more constant use since those con- 
ditions which produced them both disappeared. 
Bock Creek Valley. The largest stream tributary to the 
St. Croix in this area, is Rock creek. Rising beyond the 
boundaries of the district it occupies a deep valley extending 
westward near the south line of sections 4 and 5, T. 34 N., R. 
18 W., and then swings quite abruptly to the southwest 
through section 7 to the river. It is not wholly a late erosion 
valley. The kettles and knobs which characterize the moraine 
extend also into this valley. On either side the knoily ridges 
rise to 1,100 feet, and toward the north and east they are im- 
mediately merged into the plateau, more than 1,200 feet in al- 
titude. The bottom of the valley lies for the greater portion 
of its extent above the 900-foot contour. Below that line, 
however, there are abundant erosion lihenomena — sand flats, 
benches and terraces. The extensive level tract in S.E. | of 
See. 7 seems to indicate terracing, and should be correlated 
Math the 905-foot terrace at the Dalles. 
A slight bench at 860 feet, along the wagon road, may be- 
the local development of the 865-foot terrace of Upham* de- 
scribed as lying two miles further north. 
*Minn. Geol. and Nat. Hist. Survey, Final Report, vol. ii, 1888, p. 417. 
