LEACHED GRAVEL DEPOSITS 395 



doubtful. If the inclusions are contemporaneous with the deposition 

 of the fresh drift, why then are the inclusions oxidized and leached? 



As inclusions incorporated in the Kansan drift, these large leached 

 and oxidized sand and gravel deposits can best be explained as 

 pre-Kansan material which before being picked up and later being 

 deposited by the Kansan ice sheet were frozen into a solid mass. 

 Should this view be correct, the deposits would still be evidence of 

 a long interglacial stage. 



In any event, if there were but one exposure, one might be 

 tempted to favor the view set forth above. However, since there 

 are at least two exposures, separated by two miles, and having the 

 same stratigraphic and topographic relationships, one is led to con- 

 clude that the sands and gravels are not merely large sand and 

 gravel pockets incorporated in a till of the same age, but rather out- 

 wash deposits lying between two drifts either of the same or of two 

 different ages. 



VIEW 2. 



According to the second view, the sands and gravels are but the 

 interstratified outwash deposits between two drifts of the same 

 age and therefore represent the following conditions : 



1. An advance of the Kansan ice sheet and the deposition of the 

 lower drift, then 



2. A retreat of the ice sheet accompanied by a deposit of out- 

 wash material covering the recently deposited fresh till. 



3. A readvance of the ice depositing drift over the sands and 

 gravels which presumably were frozen into a solid mass on the last 

 advance of the ice sheet. 



4. The disappearance of the Kansan ice sheet. 



Discussion. — The above view would satisfactorily explain the 

 origin of the interbedded sands and gravels if the latter were fresh 

 as the two drifts are, above and below. If the sands and gravels 

 are contemporaneous with the two tills, then one would expect the 

 interbedded deposit to be fresh also. Is it possible that the out- 

 wash material was all leached at the time of its deposition? It 

 hardly seems conceivable that this could have been the case. Why 

 should they have been leached when the drifts are highly calcareous? 



Were the sands and gravels leached since the deposition of the 

 overlying drift? Hardly so, for the lower part of the upper till 

 is fresh; besides this drift acted as a protecting cover for the 

 underlying deposit. The till above the sands and gravels is fresh, 

 but is oxidized and leached farther up the slope of the hill. 



