Noff'fi on the Local (ieoloijtj of Manh<(t<>~ BerJidolf. <>1 



at places a conglomerate with here and there lumps of a fair 

 limonite ore. 



These clays have be^n called cretaceous by Professor X. H. 

 Winchell, State Geologist, in a piiper read before this body and 

 published in the Bnlletins. This fact first' made these clays a 

 source of interest to me and has led to a somewhat fragmentary 

 study of their ;jge and origin. 



The recent laying bare of a large surface of the Shakopee 

 formation at the cement works gave me an unusually good oppor- 

 tunity to concentrate and crystalize all tliat 1 had observed as 

 peculiar to them. From what I have seen I am led to regard these 

 deposits, not as cretaceous but as belonging to Silurian time. 



The position of these days'. — They lie in fissures of varying 

 width along joints in the Shakopee limestone. These fissures have 

 their sides rounded, polished and moulded as by trickling water. 

 The surface of the Shakopee limestone, where it has been recently 

 laid bare, at the cement works, is embossed and rounded, suggest- 

 ing roches moutonnees and indicating extensive denudation, the 

 clays are not spread out upon the upper surface of the Shako[)ee, 

 but extend down, within these fissures, at times through the Shak- 

 opee and are spread out upon the planes of bedding of the Shako- 

 pee and underlying Jordan sandstone. 



In several tissures at the cement works, the beds of clay are 

 spread out comformably to, and upon, the Jordan and under the 

 Shakopee for more than one hundred feet on either side of the 

 fissure.-. The sides of many of these fissures are lined with a layer 

 of iron rust or bog manganese of varying thickness. Upon the 

 clays and mixed with true glacial material are found, more es- 

 pecially along the Le Sueur river, the deposits of limonite to which 

 reference has already been made. 



TJie strnctare of the fissures: — The rounded sides of these 

 fissur. s indicate the action of trickling water. They are not pot- 

 holes as a cross section of any one of them shows, the clay is filled 

 into these fissures with the angle or convex side toward the upper 

 surface showing the action of a trickling stream, as a spring carry- 

 ing the clay as an impurity. In no case is the bedding of the 

 clays concentric with the sides of the inclosing, cavity as w ould 

 be the case had they been deposited from still watei-s filling the 

 cavity and holding the clays in suspension. 



In many places the clay hiis been filled in upon the Jordan just 



