CHARLES P. BERKEY 37 



0.03 mm are very common, while of course there is much finer matter. 

 The red laminae are composed of extremely fine grains and flakes. 

 There are no grains at all comparable to the sizes given above. Aver- 

 age diameters are less than 0.002 mm . 



The passage from one type to the other is sometimes gradual and 

 sometimes abrupt. As a rule, the gradual changes hold for all cases 

 in passing upward from a gray to a red lamina. The abrupt changes 

 are noted in passage upward from a red to' a gray one. Evidently 

 there is some sort of unity between each gray lamina and the over- 

 lying red one throughout the series. 



Taking, therefore, the double lamina — i. e., a gray and the suc- 

 ceeding red one above— as a unit, the following facts obtain: The 

 most irregular lines in the lamination are at the very base of the gray 

 laminae. There are sinuosities on a small scale that simulate erosion 

 unconformities. The coarsest grains seen anywhere in the material 

 are in these small embayments along this line. There is an occasional 

 streakiness of the gray laminae with the finer red material, but not 

 uniformly developed. The change to red, in rising from the base 

 of the gray lamina, takes place very gradually and gives a much 

 more even line or band than that at the base. The change to red 

 color is no more marked than the change to finer and finer grain. 

 There is no streakiness in the red layers. 



At Clam River there is some modification of these characters. The 

 proportion of gray material is greater. The upper 20 feet of that 

 deposit are decidedly gray and sandy. Lower down, however, the 

 red layers assume their accustomed character, relations, and impor- 

 tance, and are of even more than the usual thickness. 



Composition. — Much of the clay matter is so extremely fine that 

 identification in the grain is of doubtful accuracy. Among the 

 coarser fragments quartz is most abundant. Feldspar, garnet, 

 tourmaline, mica, and kaolin are also recognized. As a whole, the 

 gray laminae are extremely siliceous, while the red are by strong 

 contrast argillaceous. 



"Clay dogs," small limy concretions, occur in the upper part of 

 the deposit at Grantsburg. 



Chemical analysis shows a higher percentage of lime and mag- 

 nesia than would be expected from the color of the material. Iron, 



