PLATE XVIII. 



WATONWAN AND MARTIN COUNTIES, 1884. WARREN UPHAM. 



These counties are characterized by an undulating expanse of till, in which the 

 streams and lakes lie but fifteen to forty feet below the surface. They do not much 

 differ from Faribault county and froin the southern part of Blue Earth. Martin 

 county has no rock outcrop, although Cretaceous debris is so common that it is quite 

 probable that that formation underlies most of the county. The Potsdam quartzyte 

 appears in the township of Adrian, in the northwestern corner of Watonwan county, 

 causing an abrupt and prominent ridge that rises from 50 to 100 feet above the 

 adjoining surface. This is a part of the same ridge that extends westward about 

 twenty-two miles into Cottonwood county. The rock is hard, distinctly bedded, and 

 frequently of a red color. Its surface is glaciated in the direction S. 30 E., true 

 meridian, and S. 20 E. Aside from this quartzyte ridge it is probable that the drift 

 of Watonwan county is immediately underlain by the Cretaceous. 



A tract of country, somewhat more rolling than the rest, enters Martin county 

 at the southeast corner and extends nearly to Eairmont, having a width of about 

 five miles. This, however, does not present a strong contrast with much of the 

 central part of Martin county, and it may not be of morainic origin. 



The remarkable series of "chains of lakes" in Martin county are thought to 

 owe their origin and location to old valleys excavated in interglacial time in the 

 drift of the first glacial advance. These old valleys served as drainage courses to 

 supply the Des Moines river and mark the converging streams that united to exca- 

 vate the channel of that river at points further south. They were partly filled by 

 the drift deposited by the second glacial epoch, but were not obliterated. It is prob- 

 able that they are largely excavated in that member of the Cretaceous which Dr. 

 C. A. White named the Nishnabotany sandstone. N. H. w. 



