308 



CHARACTER OF THE COUNTRY 



a dike, the rent having been produced, probably, at the time of the upheaval and 

 bending of the strata. 



About half a mile above the first exposure, in the bed of the river, of the lower 

 conglomerate, it is underlaid by No. 448, which has an east and west bearing, and 

 dips to the north at an angle varying from 26° to 51°. It measures forty feet in 

 width across the line of strike. Next to this rock lies No. 449. Its colour is pro- 

 bably owing to the presence of chlorite. It is sufficiently soft to be worked with a 

 knife, and is occasionally used for pipestone by the Indians, though it differs mate- 

 rially from the red argillite employed by the Sioux for that purpose. It bears east 

 and west, and dips to the north at an angle of 74°. In consequence of the undula- 

 tions of this rock, and the overlying beds, which sometimes conceal it, as well as 

 the variableness of the angle of dip, its thickness could not be determined. Its 

 great thickness, however, may be inferred from the fact, that in conjunction with 

 No. 448, it is exposed in the river-bed for the distance of nearly half a mile, and 

 always dipping at a high angle. It resembles very much No. 23, brought from 

 Flint Lake. 



About a quarter of a mile above the last exposure of the conglomerate (No. 441), 

 the shales disappear, and red clay, marls, and drift, make the river-banks until the 

 first or Lower Falls are reached. At this place, No. 450 is exposed, bearing east 

 and west, and dipping south at an angle varying from 80° to 88°. It is traversed 

 by veins of No. 452, from two to ten inches wide, having an east and west direction. 

 This last rock alternates with beds of No. 451, and contains small, irregular cavities, 

 filled with iron pyrites and calcareous spar. 



Proceeding in the direction of the upper end of Grand Portage, these slates take 

 on the character of No. 453 ; and still further up the river, bear a great resemblance 

 to some of the altered slates found on Mud Lake. Some of the beds are highly 

 altered, and indicate the near vicinity of intrusive igneous rocks, although no such 

 beds or dikes of trap were discovered among them as occur at numerous other loca- 

 lities in the same range. Near the upper end of Grand Portage, the argillaceous 

 slates bear east 11° north, and west 11° south, and dip east of south. At one point, 

 the beds are nearly vertical for some distance, and the dip is reversed. 



On " Six Pause Creek," about three miles distant, in an east by south direction, the 

 slates bear northeast and southwest, and appear to have been altered by intrusive 

 trap ; and on a small creek about three miles south of this place, another exposure 

 was found near the summit-level of the portage, bearing east and west, and dipping 

 to the north at an angle of 40°. 



Between Grand Portage and Knife Portage, the blue argillaceous slates continue 

 to show themselves in the river-banks, and also in small islands, rising from ten to 

 twenty feet above the water. 



It will be perceived from these details, that after leaving the exposure of conglo- 

 merate (No. 441), the only rocks seen in place were argillaceous and magnesian 

 slates ; although it is highly probable that they are traversed by trap rocks in that 

 distance. I am led to this conclusion from the high angle at which they dip in 

 several directions, the changes of bearing, the evident alteration produced in some 

 of the beds by igneous action, and the fact that trap rocks were found associated 



