36 LAMINATED CLAYS OF GRANTSBURG, WIS. 



Croix, on Snake River about 6 miles above its mouth, a deposit of 

 laminated clays that might be interpreted as a marginal facies, but 

 with no intervening exposures there is doubt about this connection. 



Although exact boundaries, therefore, are not known, an extent of 

 at least 20 miles north and south, and a width of 10-15 miles, are 

 certain. Thus the area known to be underlain by these clays is 

 about 250 square miles. The probable area is still greater, but in 

 some directions the margins are hopelessly buried beneath heavier 

 glacial deposits. 



Thickness. — At Grantsburg 15 feet of the stratified clays are 

 exposed in the workings of the Terra Cotta Brick Co. Mr. Ira C. 

 Jones, the manager, at the writer's suggestion, bored entirely through 

 the deposit, and reports a total of 35 feet at that point. There is, 

 however, at the same place clear evidence of the removal of some of 

 the topmost material by later ice-advance. How much should be 

 accounted for in this way no one can tell, but the original thickness 

 was certainly more than 35, and probably less than 40, feet. 



Near the mouth of Wood River, as noted above, the same deposit 

 is 5 feet thick. 



On Clam River, with 40 feet exposed, the deposit is not entirely 

 cut through. An undulating habit of the lowermost laminae, however, 

 seems to indicate proximity to the floor. 



Character. — These clays are all strongly laminated. The laminae 

 vary in thickness from a mere film to several inches in different parts 

 of the deposit, but are comparatively uniform in any particular zone. 

 Their average thickness in the upper part of the deposit is about a 

 quarter of an inch. The average thickness nearer the middle is 

 about one-tenth of an inch. Less uniformity is observable near the 

 top than in any other zone. 



The lamination is extremely regular and approximately horizontal. 

 Small crumplings or bunchings occur, but are rare. 



The general color is red from top to bottom. On closer inspection, 

 however, the laminae are seen to be of two types — a deep red one, and 

 a gray, which alternate without exception throughout the deposit. 



Very perfect water-sorting is evident from a study of these indi- 

 vidual laminae. The gray ones are comparatively coarse-grained, 

 containing maximum diameter of o.o6 mm . Diameters of 0.02 to 



