Druvih'iis coiifaiiiirig Modified Drift. — UpJuiin. 88:> 
level. Between ( -hengwatana and Taylor's Falls tliere is a 
trough which is the continuation of the lake Superior syncli- 
nal and which probably swings southward here.* 
Tile strike of the exposures of diabase at St. Croix Falls, if 
projected beyond the area, passes 10 miles to the east of Still- 
water. A dip of 15 degrees carries the strata down over 1,40U 
feet per mile, so that, if this angle were constant toward the 
southern limits of these rocks, they should not come within 
1.3,000 feet of the surface at Stillwater. In fact they would 
pass to a lower level in the distance of a single mile from the 
last outcrop in the Dalles area than is actually reached at 
Stillwater. And the tendenc}^ of the strike to swing even 
farther eastward, as has already been noted, would serve only 
to increase the discrepancy. 
Under these conditions it is clear that there is an extensive 
trough between Taylor's Falls and Stillwater which may be 
considered a secondary fold beyond the limits of the major 
synclinal fold of the lake Superior axis. 
Unconformity. The unconformity between the Keweena- 
wan eruptives and the Cambrian sedimentaries is nowhere more 
clearly marked than at Ta3Hor's Falls and St. Croix Falls. 
Wherever the actual contact of these two formations is seen, 
evidence is clear of the immense time and erosion interval be- 
tween them. Four or five such contacts are known in the ex- 
posures within the immediate vicinity of the Dalles on both 
sides of the river. 
Differences of erosion of adjacent areas, amounting to 400 
feet, accomplished previous to the deposition of the earliest 
shales, is shown along the present course of the St. Croix 
river. This is probably no exceptional occurrence, but is a 
fair example of the general erosion previous to complete sub- 
mergence. 
DRUMLINS CONTAINING OR LYING ON 
MODIFIED DRIFT. 
By Warren Upham, St. Paul, Minn. 
The occurrence of beds of sand and gravel inclosed within 
oval accumulations of till, which in all other respects appear 
to be typical drumlins, has been reported in several of my 
*R. D. Irving: The Copper-bearing Rocks of Lake Superior, U. S. G. 
S., Monograph v, 1883, p. — and map. 
