The granitical series of strata, which is apparent in northern New York in the Kayaderasseras Mountains, and at the Thousand Islands of the St. Lawrence, reappear on the north shores of Huron and Superior, underlie the bed of the latter, and rise up in the rough coast between the Chocolate River and Kewaiwenon, cross the Mississippi at the Petite Roche, above the Falls of St. Anthony, and put out spurs as low down as the source of the Fox, the St. Croix, and the head of the St. Peter's Rivers. These glimpses of some of the leading points in the geological structure of the regions visited, will enable you to follow my details more understandingly. These details begin at Detroit. From this place the expedition passed, by water, along the southern shores of Lakes St. Clair, Huron, and Superior, to the Fond du Lac; thence, up the River St. Louis, to the Savanne summit. Thence we proceeded across the portage to Sandy Lake, which has an outlet into the Mississippi, and followed up the latter, through the lesser Lake Winnipek, to the entrance of the Turtle River, in Cass, or upper, Red Cedar Lake, which is laid down by Pike in north latitude 47° 42´ 40´´.[210] The state of the water was unfavorable to going higher. [210] Pike's Expedition. This observation is corrected by Capt. Douglass to 47° 27´ 10´´; the point of observation being, however, a few miles south. From this point, which formed the terminus of the expedition, we descended the Mississippi, making portages around the Falls of Pekagama and St. Anthony, to Prairie du Chien. An excursion was made by me down the Mississippi to the mineral district of Dubuque. We ascended the Wisconsin, to the portage into the Fox River, and traced the latter down to its entrance into Green Bay. At this point, the expedition separated; a part proceeding north, through the bay, to Michilimackinac, and a part going south, along the west shores of Lake Michigan, to Chicago, the latitude of which is placed by Capt. Douglass in 41° 54´ 06´´. At this place, a further division took place. Dr. Wolcott, having reached his station, remained. Governor Cass proceeded across the peninsula of Michigan to Detroit on horseback, leaving Capt. Douglass and myself to complete the survey of Lake Michigan. We rejoined the northern party detached at Green Bay, under Mr. Trowbridge and Mr. Doty, at Michilimackinac; and, after repassing the southern coast of Lakes Huron and St. Clair, reached Detroit.