384 



DESCRIPTION OF THE COUNTRY BORDERING 



A section of the rocks immediately below the mouth of this river, is exhibited in 

 the annexed cut. The underlying rock is a shaly amygdaloid ; above that, a bed 



c. Shaly amygdaloid. 



d. Tnlcanic grit. 



c. Volcanic grit, with shales. 



b. Breccia. 



a. Shaly amygdaloid. 



of amygdaloidal breccia, and over that, a bed of volcanic grit (No. 146). These 

 beds are all somewhat disturbed, and traversed by veins of calcite, in one of which 

 I found traces of green carbonate of copper. In proceeding from the Lake, the 

 metamorphosed shales become much thickened, and are associated with beds of 

 altered grit, and occasional exposures of a corrugated bed. They form the shore of 

 the first two bays, overlaid by a bed of trap. In the third one, there are altera- 

 tions of shale and thin beds of trap (No. 133), which are greatly disturbed, and dip 

 south and southwest. At the point of this bay, is a beautiful exhibition of basaltic 

 columns projecting into the Lake, of which the following sketch by Major Owen 

 will give a much better idea than a written description. The exposure is about 



BASALTIC COLUMNS, LAKE SUPERIOR. 



twenty feet in height, and the columns rest on beds of metamorphosed grit, over- 

 lying decomposing amygdaloidal shales ; showing conclusively, I think, that the 

 basalt here is an overflow, and does not occupy the original site of eruption. 



Beyond this point the exposures are low, and consist of metamorphosed shale and 

 sand-rock, until the middle of the bay is reached, where they are cut through by a 



