QUATERNARY FORMATIONS THE DRIFT. 235 



dation for agricultural industries; a resource for the many, not the 

 few a wealth for the people. 



Brick. Second only to this in importance are the building mate- 

 rials furnished by this formation, prominent among which are the de- 

 posits of brick clay. These belong to two classes, the light colored and 

 red clays. The former are lacustrine, or fluviatile deposits, derived from 

 the wash and redeposit of the bowlder clay, and occur within the area 

 covered by that formation. They are local accumulations, and are of 

 various bluish drab and yellowish hues. A portion of these clays 

 burn to a beautiful cream color, while other portions become red. 

 The superiority of the former in texture as well as color has almost 

 entirely excluded the products of the latter from the market. The 

 second class, the red clays, are simply those portions of the red clay 

 deposits already described as are sufficiently free from pebbles for the 

 purpose. Such portions are almost invariably found at the junction 

 of the beach formations with the main clay deposit. At that horizon 

 are beds of clay and sand, and of the two variously mingled, thus fur- 

 nishing the two essential ingredients of brick manufacture in the 

 most convenient proximity and association. Very frequently a stra- 

 tum mingled in the proper proportion by nature may be found. This 

 is a definite and wide spread formation, and affords the most unlim- 

 ited quantities of excellent material. 



Notwithstanding its native red color, it burns to a very desirable 

 white or cream hue. This fact has very justly excited not a little 

 surprise, none the less so because a portion of our light colored clays 

 burn red. 



That the light color of the brick is not due to the absence of iron 

 is evident from the manifest presence of that substance as the color- 

 ing matter of the clay, and this has been confirmed by analysis. It 

 has been observed that the brick frequently contain small black, 

 glassy points, and it has been thought that, in the progress of burning 

 a process of segregation took place, whereby the iron was concentrated 

 in these concretions, and this view was apparently confirmed by the 

 fact that the brick are red up to a certain stage in the burning. The 

 recent investigations l of Mr. E. T. Sweet upon the Milwaukee brick 

 have thrown much additional light upon the subject, though not 

 specifically applicable to the red clays, since the brick of the " Cream 

 City" are made from a light colored clay. For the purpose of com- 

 parison, Mr. Sweet analyzed a specimen of the Madison clay, which 



1 Paper read before the Wisconsin Academy of Sciences, Arts and Letters, February 

 15, 1877. 



