SILVERIA (?) FORMATION AND OTHER SILT DEPOSITS. 117 



coal shaft near Sparta in eastern Randolph County, has been published by 

 Prof. J. M. Nickles. 1 The Pleistocene deposits are as follows: 



Section of Pleistocene beds penetrated by the Isabella Thompson coal shaft near Sparta, 



Illinois. 



Feet. 



Soil and clay 3 



Yellow clay 17 



Blue clay 3 



Quicksand •_ 4 



Silt 2 



Gravel 4 



Silt Si 



Sand and gravel 6A 



Drab or mouse-colored silt 11 



Concrete or bardpan 4 



Fine gray sand 6 



Sand and clay mixed 6| 



Silt 2i 



Bowlder clay 6A 



Fine gravel i 



Bowlder clay If 



Laminated clay, containing wood 5 



Total drift 90 



In this section there appears to have been an alternation of glacial and 

 lacustrine deposition without distinct evidence of long interruption. The 

 laminated clay at the base of the series contains a large amount of wood, 

 specimens of which have been sent to the writer by Professor Nickles, but 

 which await specific identification. 



Borings for coal and water in the Big Muddy Valley in the vicinity 

 of Murphysboro usually penetrate a large amount of sand. As this valley 

 does not appear to have been obstructed by the ice invasion the sand can 

 not be referred with any certainty to lacustrine conditions. It seems more 

 probable that it is an indicator of the weakness of the currents of the stream. 



The tributaries of the Wabash in southeastern Illinois are usually 

 filled with sand or silt, and these open southward in such manner as to 

 avoid obstruction by the advancing ice sheet. The filling probably may 

 be taken as an index of the weakness of the currents of the stream just 

 before the ice invasion. It may be remarked in this connection that the 

 filling of the valleys of southern Illinois apparently opposes the somewhat 

 popular hypothesis that there was a period of high elevation and vigorous 



Final report Illinois Board World's Fair Commissioners, 1893, pp. 200, 201. 



