18 THE GEOLOGY OF MINNESOTA. 



[Ochagach, 1730. 



Le Sueur took a quantity to France for assay, it is not likely that he 

 wilfully falsified the facts as to its origin and nature. There can be no 

 question of the existence of both green and blue earth in that vicinity. 

 The shales of the Cretaceous are common in that part of the state, and 

 there is also a clayey deposit, supposed to be of the Cretaceous, found lying 

 unconformably in eroded places in the Cambrian limestones of that valley. 

 The hard, black, burnt crust mentioned, which, on being scraped, exhibited 

 the copper, can be no other than the ironstone incrustation that covers the 

 Cambrian limestones, as seen at Mankato, wherever the Cretaceous clays lie 

 unconformably over them. 



OCHAGACH'S MAP. 



The oldest map of the region west of lake Superior was traced by a 

 chief of the Assiniboines, named Ochagach, for Verendrye, in 1730, and 

 was taken by Verendrye to the governor of Canada to induce him to equip 

 an exploring expedition in search of a passage to the western ocean. This 

 map was sent to Paris and deposited in the Archives de la Marine. A 

 reduced transcript of this map is given below (Fig. 1.), derived from a fac- 

 simile tracing in the Department of American History of the Minnesota 

 Historical Society, through the courtesy of Mr. Neill. It was reproduced 

 on the margin of Buache's map of 1754, and its contents are also incor- 

 porated in Buache's general Carte Physique. (V. Plate 4.) It gave rise 

 to the important and extensive explorations of Sieur Verendrye and his 

 sons and nephew (Jeremaye), which extended through several years and 

 covered the valleys of the Assiniboine and Saskatchawan, as well as those 

 of the upper Missouri and the Yellowstone, to the " shining mountains." 



The water-course rudely represented on this chart, extending westward 

 from lake Superior, is that which afterward became the international 

 boundary. The river marked "R. de fond du L. Superieur" is evidently 

 that which is now known as Vermilion river, north of Vermilion lake, and 

 derived its designation by Ochagach from the fact that it furnished the 

 main route, for east-bound canoes, to the head of lake Superior and the 

 south shore of that lake ; and, for a similar reason, that marked " Missis- 

 sipi" represents the Big Fork river. The "Fleuve de 1'ouest" is evidently 

 the present Saskatchawan river, flowing into lake Winnipeg from the west, 



