402 DESCRIPTION OF THE COUNTRY BORDERING 



continued along the bottoms of the bays below, until it finally reaches Pigeon River. 

 It is intersected in this distance, at various points, by narrow dikes, which contri- 

 bute to the formation of the points between Grand Portage and Pigeon River. The 

 last dikes differ, lithologically, from the one in question, and are easily traced across 

 the slates and the great greenstone dike. 



Near the west end of the ridge, one of the prismatic dikes, discovered by Major 

 Owen on the shore of Grand Portage Bay, crosses it, bearing east and west. This 

 dike is thirteen feet wide. Between the ridge and the Lake, the ground is low, 

 and as the ridge is approached, the dike stands up in the woods like a wall, with 

 all the regularity of masonry, as seen in the preceding sketch, by Major Owen. The 

 prisms are nearly horizontal, and from a foot to two and a half feet in diameter. 

 In addition to the two dikes discovered here by Major Owen, and which run due 

 east and west, I found another in the woods, further west. It does not show itself 

 on the lake-shore, but traverses the low grounds in the form of a great wall, fifty 

 feet in height. It bears east .15° north (No. 646), and is sixteen feet wide. It 

 finally enters the first high escarpment north of the Lake, formed by between 

 seventy and eighty feet of slate, overlaid by a bed of trap. These dikes all cut 

 across the subordinate ridges, and continue on to the main range. 



The valley of the first stream, a tributary of Pigeon River, which crosses Grand 

 Portage, is bounded on the lake side by a high range of rocks bearing northeast and 

 southwest, six hundred and fifty feet high, from which four other ranges are visi- 

 ble to the northwest, all having, apparently, the same bearing. From the summit 

 of this ridge, four miles distant from the lake, the spectator commands an exten- 

 sive bird's eye view, as far as the mouth of Pine River, and the ranges north of it, 

 in Canada. This scene is well depicted by view 1, on PI. 1, N., looking to the 

 north. 



From the top of another and higher ridge, southeast of the one we first ascended, 

 looking south, we could see the Lake. The northwest side of all these ridges have 

 mural escarpments, from one hundred and fifty to two hundred and fifty feet in 

 height, the top rock being greenstone, and the bottom argillaceous and siliceous 

 slates. Occasionally, fissures five or six feet in width are found in these ridges, 

 through which the escarpments may be ascended. In most cases they have been 

 occupied by spar veins, carrying oxide of iron, and their general direction is north- 

 west and southeast. 



Further west on the portage, large masses of greenstone are occasionally found 

 resting on the slates, and several low slate ridges occur in the neighbourhood of 

 the river. Where the portage strikes Pigeon River, the slates are unaltered, and 

 dip southeast at an angle of 8°. 



From the nature of the country it is not possible to trace many of the narrow 

 dikes with certainty for great distances. It is believed, however, that most, if not 

 all, of those seen on the lake-shore, traverse the ridges lying between the Lake and 

 Pigeon River, and form the numerous spurs having a north-and-south bearing, and 

 which, upon being traced to the high escarpments, are found to be formed by nar- 

 row dikes. At some localities they start from the lake-shore in the form of high, 

 narrow Avails, and crossing the low grounds, from which the bedded rocks have been 

 removed by denudation, enter the ridges, cut through them, and are found pursuing 



