APPENDIX. 319 



bearings may be attributed, appears to have thrown up the 

 trap-rocks of the Pic, of the Porcupine chain, of the Isle Royal 

 group, and other trap islands, and the long peninsula of Ke- 

 weena. This system of forces appears to have spent itself from 

 the northeast to the southwest. The shocks brought with them 

 the elements of the copper and other metallic bodies which cha- 

 racterize the trap-rock. They exhausted their power, on the 

 American side, west of the granitic tract of Chocolate and Dead 

 Rivers, and the Totosh and Cradle-Top Mountains. The most 

 violent disturbance took place at the west of the Keweena Pe- 

 ninsula, and thence it was propagated in the direction of the 

 higher Ontonagon, the Iron, and the Montreal rivers. 



This disturbance of the level of the sandstone produced undula- 

 tions, which are observable on the St. Mary's, where the variation 

 from a level is not more than eight or ten degrees. They left 

 portions of it — as between Isle au Train and the Firesteel River — 

 undisturbed; and they threw other portions of it — as between 

 Iron and Montreal rivers — almost completely on their edges. 



The entire north shore from Gargontwa to the old Grand 

 Portage, inclusive of the Michepicotin and Pic regions, cannot be 

 particularly alluded to, as that part of the coast was not visited ; 

 but the accounts of observers represent it as consisting of trap- 

 rocks. Without the application of such forces, it appears impos- 

 sible to understand the geology of this lake, or to account for the 

 sectional and disturbed formations. 



The lake itself, whose depth is great, and which has an. extreme 

 length of about 500 miles, by an extreme width of some 180, is 

 endowed with powerful means of existing elemental action. This 

 consists almost entirely of the force of its winds and long, sweep- 

 ing waves. Its bottom may, in this light, be looked upon as an 

 immense mortar or triturating apparatus, in which its sandstones, 

 trap-boulders, and pebbles are driven about and comminuted. 

 This power has greatly changed its configuration, and the process 

 of these mutations is daily going on. 



It is only by such a power of geological action that we can 

 account for the poAverful demolitions and inroads which it has 

 made upon some parts of its southern borders. The coasts of the 

 Pictured Rocks, which have a prominent development of about 

 12 to 15 miles, consist in horizontal strata of coarse gray sand- 



