180 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
belonging to a different rock series. Speaking of the Bohemian Range, Dr. 
C. T. Jackson says: 
* * * if the rock was not connected with the more hornblendic trap, and in the 
same line of direction, bursting through the same kind of sandstone strata, I should 
feel disposed to regard it as of more ancient origin. Indeed, I am far from being sat- 
isfied that it is not more ancient, for the limited exposure of the rocks does not allow 
any geologist to be too confident in his opinion respecting its age. 
Foster and Whitney say that the Bohemian Range— 
differs from the northern both in lithological character and in the mode of its occur- 
rence. While the former, before described, is composed of numerous beds of trap, 
in the main of the amygdaloid and granular varieties, interstratified with the detrital 
rocks, the southern range consists of a vast crystalline mass, forming an anticlinal axis, 
flanked on the north by the bedded trap and conglomerate, and on the south by con- 
glomerate and sandstone. The contour of the unbedded trap is also very different 
from that of the bedded trap. We nowhere recognize the stair-like structure in the 
hills; they are either dome-shaped or rounded.’ 
Elsewhere Foster and Whitney speak of the Bohemian Range as formed 
by a later outflow than the more northern beds, and as having forced the 
more northern beds into their present inclined position. Charles Whittlesey 
speaks of the rocks of the Bohemian Range in the same vein, though he 
calls them Huronian, and hence older than the more northern beds; he re- 
fers also to the anticlinal structure described by Foster and Whitney.* 
Still more recently Dr. T. S. Hunt speaks in the same way of the rocks of 
the Bohemian Range, and quotes approvingly the opinion of Mr. Ernest 
Gaujot to the effect that they belong to an older series.* 
Before visiting the Bohemian Range myself I was rather inclined to 
suppose that its rocks might possibly be, in part at least, more ancient than 
the typical Keweenawan, and more especially to believe in the existence 
there of an anticlinal axis, as described and pictured by Foster and Whit- 
ney; the existence of which anticlinal I conceived might help to explain 
1 Report on the Geological and Mineralogical Survey of the Mineral Lands of the United States 
in the State of Michigan.” Ex. Doc. No. 5, p. 473, 31st Congress, 1st sess, 
?Geological Report on the Copper Lands of the Lake Superior Land District, Michigan, 31st Con- 
gress, Ist session, 1849 to 1850, Ex. Doc. No. 69, p. 64. 
3“Physical Geology of Lake Superior. Proc. Am. Assoc. Ady. Sci., Detroit meeting, August, 
1875, p. 71.” Col. Whittlesey here speaks of the Bohemian Range rocks as ‘‘intrusive Huronian,” and 
yet as having caused the tilting of the more northern rocks of Keweenaw Point, so that it is difficult 
to tell exactly what he does mean. 
4Special Report on Trap Dykes and Azoic Rocks of Southeastern Pennsylvania, 1878, p. 230. 
