324 C. W. HALL — KEWEENAWAN AREA OF EASTERN MINNESOTA 



doubt. They are therefore here regarded as one and the same, and no 

 discussion of their age will be entered upon. 



THE SAINT CROIX COPPER RANGE 



It is in the small area lying within townships 42 and 43, range 13 

 west, and northeastward that the highest Keweenawan rocks of the dis- 

 trict lie. Along the north side of the Saint Croix river and within the 

 bed of the stream is seen a series of sandstones and conglomerates ex- 

 tending for some miles. Strong describes these rocks, according to 

 Chamberlin, as follows : They consist " of a red sandstone approaching 

 in its variations a fine conglomerate on the one hand and an arenaceous 

 shale on tlie other, and containing, embedded in it, fragments and thin 

 leaves of shale. An examination of the granular ingredients shows that 

 it was derived mainly from the crystalline igneous beds of the series. Its 

 dip appears to be 10 degrees to the southeast." * The highest beds of the 

 Keweenawan in this entire district are, according to Irving, at the Indian 

 village in the northwest quarter of section 21, township 42, range 14 west.f 

 These beds are ma})})ed by him and the Wisconsin geologists as Upper 

 Keweenawan. It would seem that they disappear before the Minnesota 

 exposures are reached. The Kettle River lava flows and intervening 

 conglomerate beds are so like all exposures of the Lower Keweenawan 

 that they have been with but little reserve relegated to that subdivision. 

 If these be Lower Keweenawan, there is no Upper Keweenawan in this 

 part of Minnesota. 



KETTLE RIVER 



Along the Kettle river there are many interesting exposures of lava 

 flows and conglomerates. The westernmost are in section 22. township 

 41, range 20 west, mentioned in the discussion of the western fault line. 

 On both sides of the river almost a contact is seen between the diabase 

 and the younger Cambrian sandstones. The ex])osures extend on both 

 sides of the river for nearly a mile. On the north side in a ravine dry 

 for the most of the year the amygdaloidal diai^ase stands up in a sharp 

 line of exposure nearly in the direction of the strike, di])])ing some 

 40 to 50 degrees to the east. On the west bank of the ravine, and scarcely 

 10 feet away from the amygdaloid, the broken sandstone stands in an 

 abrupt escarpment. The sandstone must show not less than 75 feet with 

 no evidence of the bottom layers in sight. Along the entire distance of 

 the contact the attitude of the sandstone is that of a greatly disturbed 



* Geology of Wisconsin, vol. iii, 1880, p. 424. 



t R. D. Irving : The copper-bearing rocks of lake Superior, Monograph v, U. S. Geol. Survey, 

 1883, p. 24G. 



