TOPOGRAPHY. 655 



vines. Such, in brief, appears to be the theory of the formation of 

 streams in the Lead region. Its application is easy, and would be as 

 follows : 



The Wisconsin river from. Mazomanie, to its mouth near Prairie 

 du Chien, is the most conspicuous example and illustration of the 

 foregoing remarks. 



Although the surface of the country, in its present condition, does 

 not permit the accurate delineation of the former lines of outcrop, of 

 the paleozoic formations; yet a sufficient number of outliers remain, 

 to show us that they must once have covered the country, far north 

 of where they are at present found. The existence of Niagara lime- 

 stone, in a thickness of about one hundred and forty feet at the Platte 

 Mounds, and probably the full thickness of the formation at the Blue 

 Mounds, warrants us in supposing that the former outcrop of the un- 

 derlying Cincinnati group was at least as far north as the present bed 

 of the Wisconsin river. 



The valley now occupied by the river, from Mazomanie to Blue 

 river, is very nearly that of the present line of strike of .the Lower 

 Silurian formation, and, although from there the strike of the lower 

 members (of which outliers still remain) appears to bear rather more 

 to the northward, yet, observations on the dip of the Cincinnati group, 

 in such occasional outliers as remain, lead me to believe that its origi- 

 nal strike was approximately in a southwesterly direction, from Blue 

 river to the Mississippi. 



Assuming, then, that the Cincinnati group once had its northern 

 outcrop where the river now runs, or in a line parallel to it, in that 

 vicinity, the surface waters would easily erode a channel in the soft 

 and friable shales which, to a great extent, compose this formation. 



In fine, the whole process of formation previously described would 

 take place. On the north side it had, as now, its principal tributary 

 streams, the Kickapoo, Knapp creek, Eagle river, Pine river and Bear 

 creek, in their present localities, and approximately their present 

 length. On the south of the river, however, the principal watershed, 

 already referred to, was probably quite near the river, from which 

 position it has receded to the place it now occupies. The Green river, 

 Blue river, Otter, Mill and Blue Mound creeks were small and insig- 

 nificant streams; which, by the gradual process of erosion, have in- 

 creased to their present size and length; but even now, are small when 

 compared to the northern tributaries. 



A further effect was to shorten the Grant, Platte, and Pecatonica 

 rivers, by the gradual southwesterly recession of the watershed, and 

 the lowering of the latter by the denudation of the Niagara limestone 



