4 o LAMINATED CLAYS OF GRANTSBURG, WIS. 



The larger development of sands immediately upon and after the 

 deposition of fine clays of so great extent seems to indicate a long- 

 continued assorting of materials, carrying the fine matter forward 

 and leaving the coarser behind, until a final movement of the chief 

 agency brought them both together a second time — but this time in 

 separate beds. The prevailing sandiness of the upper portion of the 

 laminated deposit at Clam River leads one to regard that direction — 

 i. e., the north or northeast — as nearest to the general supply. This 

 is the region also that constitutes the typical sand barrens of northern 

 Wisconsin. The long, assorting process must have been as promi- 

 nent a genetic factor with them as the type of bed-rock from which 

 they were obtained. 



The laminated clays. — The laminated clays are no doubt a lake 

 deposit. The uniform succession of laminae, the relationship between 

 the red and gray, and the constancy of their characters lead one to 

 look for some uniformly periodic cause of formation. 



The presence of comparatively large grains throughout the gray 

 laminae shows a continuance of supply of new material during its 

 accumulation at least, while the presence of some streakiness of 

 finer red matter occasionally in them indicates fluctuations or lulls 

 within this period of supply. 



The absence of all large fragments in the red laminae, their uni- 

 formity of succession, and their gradual increase in fineness of grain 

 seem to argue a period of complete cessation of supply from with- 

 out and complete protection from disturbances. 



This periodic supply, then, must mark either successive storms or 

 successive thawings of neighboring glacial ice. If the latter, then 

 the period is seasonal, and each unit of lamination, a gray and a 

 succeeding red layer together, represents a year of time. On this 

 supposition, the summer thawings of the glaciers furnished silt to 

 the lake then covering the Grantsburg area, and left behind great 

 quantities of coarser materials to be later spread as the poorest of 

 northern soils. Winters checked the supply, coated the lake with 

 ice, and in this quiet season the finest sediment settled down in the 

 uniform red laminae of the clay deposit. 



The deposits themselves have further evidence on this point. It 

 is scarcely conceivable that a supply controlled by spasmodic periods, 



