LAMINATED INTERGLACIAL CLAYS OF 

 GRANTSBURG, WIS. 



[with chronological deductions.] 



CHARLES P. BERKEY 



Columbia University 



Grantsburg, Wis., is in Burnett county. The St. Croix River 

 forms the western boundary of the county, separating it from Minne- 

 sota. Two large streams enter the St. Croix from the east; one, 

 known as Clam River, crosses the central portion of the county, and 

 the other, Wood River, crosses well toward the south. Both, in their 

 lower courses, cut entirely through the capping drift deep into a 

 stratified clay deposit that forms the subject of this paper. 



At all points the clays lie beneath a later and coarser sheet of either 

 modified drift or till, or both. This capping varies in thickness from 

 a few feet to possibly 50 feet, or even more. Yet the general surface 

 of the country is extremely level over large tracts. Swamps and 

 so-called meadows of immense size are a common feature. But 

 the remainder of the district known to be underlain by the clay bed 

 is typical sand barrens. That the clays extend also beneath the 

 adjoining morainic belt forming the southeastern margin of the 

 sand tract is indicated by characters in the deposits themselves, 

 although their actual presence in that direction is not a matter of 

 observation. 



Extent. — One margin of the deposit is near the mouth of Wood 

 River. The thickness there at its best exposure is only 5 feet. The 

 broad St. Croix valley then cuts into this margin, and beyond no trace 

 of the clays has yet been found. Exposures on Clam River lie 15-18 

 miles northeastward from those to be seen on the Wood. A total 

 thickness there of over 40 feet seems to indicate that the margin in 

 that direction is still some distance away. The same is true of the 

 eastward extent, as noted above, while toward the west the broad 

 St. Croix valley has destroyed the southern portion, at least on that 

 side. There is, however, at one point on the west side of the St. 



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