192 PHYSICAL GEOGRAPHY. 



and extends along part of its south coast until lost under 

 newer deposits, may be learned from the subjoined extract 

 of a " Report by Dr. Owen, geologist to the States of 

 Iowa and Wisconsin." * 



* " The protozoic strata form sections on the Mississippi for an 

 average distance, in a direct line, into the interior of Wisconsin, of 

 from fifty to seventy-five miles, or up to the low falls of the principal 

 eastern tributaries of that river, -where the crystalline rocks first 

 appear. In this part of the country the igneous ranges do not rise 

 into elevated mountains, but, on the contrary, they are seldom seen 

 except in the immediate cuts of the streams, being, for the most part, 

 covered with drift. The character of the country generally, towards 

 the summit levels leading to Lake Superior, is a succession of ter- 

 races of moderate elevation, chiefly composed of drift, having a 

 nucleus, no doubt, of granite, syenite, or hornblende rocks ; but 

 these protrude only occasionally. At intervals the streams are ruffled 

 into rapids, being filled with boulders which materially obstruct their 

 navigation. A portion of these boulders may have been transported 

 from great distances, but the greater part appear not to be far re- 

 moved from their parent rock. It is a matter of surprise that so large 

 an area of the interior of this district, and indeed of the sources of the 

 Mississippi generally, should be level tamarack and cedar swamps, 

 since, on approaching a great water-shed that gives rise to one of the 

 greatest rivers in the world, one is led to anticipate a country with 

 physical features of quite a different character. Interposed between 

 the crystalline and igneous rocks of the interior of the district and 

 the lowest sandstones, some green and red schistose beds have been 

 observed at different localities. These appear to have been derived 

 from the decomposition and detritus of the more easily disintegrating 

 felspathic granites. The lower beds of sandstone adjacent to the 

 igneous outburst are not unfrequently changed to hard quartzite." .... 

 " The highest ranges of the Wisconsin side of Lake Superior, situated 

 from ten to sixteen miles from its south shore, arc estimated to be 

 near 1,000 feet above the lake, and are formed of hornblende rocks, 

 metamorphic slates, syenite, and trap. No organic remains have been 

 detected in the great mass of sandstone bounding this part of the 

 lake whereby its geological era may be determined. On the west 

 side of the Mississippi, north of the Winebago reserve (Minesota), and 

 as far north as St. Peter's river, limestone, with underlying sandstone, 

 prevails to the extent of half a degree of longitude." 



