Reviews. 



SUMMARIES OF THE LITERATURE OF STRUCTURAL 

 MATERIALS. II. 



Edwin C. Eckel. 



Berkey, C. P. Origin and Distribution of Minnesota Clays. Amer. Geol- 

 ogist, Vol. XXIX, pp. 1 71—177, March, 1902. 



Residual clays, derived either from feldspathic rocks or from limestones, are of 

 slight importance in Minnesota. The larger clay working establishments of the state 

 are using shales, stream deposits, or glacial lake clays ; the smaller brick plants of 

 local importance use till or loess. 



The shales of most importance are those of the Ordovician and Cretaceous. The 

 Ordovician shales are found only in the southeastern portion of the state. Most beds 

 are too calcareous for use, but one company in Minneapolis utilizes Ordovician shales 

 in the manufacture of an exceptionally fine line of front and pressed brick. The 

 Cretaceous shales are used in the manufacture of stoneware at Red Wing. 



The clays may be divided as to origin into glacial till, glacial lake clays, glacia* 

 stream deposits, recent alluvial deposits, and wind deposits. 



Locally the till includes clay deposits of workable size. These clays differ in 

 character according to the drift in which they are inclosed. The "gray drift" which 

 has been brought by ice movements from the north and northwest carried fine-grained, 

 calcareous, light-burning clays, though in places weathering may have removed 

 enough lime to give red-burning clays. The "red drift" brought in from the north 

 and northwest carries coarser grained clays with an excess of iron, which consequently 

 burn red. 



Clacial lake clays, laid down in quiet water in interglacial periods, are confined 

 to the eastern border of the state, where extensive deposits occur and are worked on 

 a large scale. 



Clacial stream deposits include the river silts deposited during the withdrawal of 

 the ice. Clays of this type are worked on the Mississippi river between Minneapolis 

 and Little Falls, and on the Missouri river between Shakopee and New Ulm. These 

 clays are obtained from the terraces bordering the present river channels, and burn 

 cream or gray. They are the most important of the Minnesota clays, large plants 

 using them being located at Chaska and Minneapolis. 



Recent alluvial deposits occur in the same areas as the last class and in many 

 cases cannot be differentiated from them. 



Most of the smaller brick plants of the state work on material obtained from loess 

 deposits. The clayey loams of this class are widely distributed, but are nowhere of 

 great thickness or value. 



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