Pleistocene to P re-pleistocene of Mississippi Basin. 373 



Even in the silts and loams that overlie the gravels and 

 underlie the weathered and humus-marked horizon which 

 divides the gravels, sands and silts below, from the loess above, 

 microscopic examination fails to reveal the particles of the 

 various complex silicates and dolomite which characterize the 

 loess above, and which characterize all glacial silts with which 

 we have any familiarity. It is to us wholly incredible that 

 these sands and silts could have been deposited by a river 

 originating in a glaciated tract, without including these char- 

 acteristic products of the glacial grinding. 



If it be suggested that the gravels date from the interval 

 between the two glaciations of the first glacial epoch, and so 

 from a time when the streams did not carry glacial waters, the 

 case is no better. For on this hypothesis, even if the main 

 stream did not carry glacial waters at the time of the deposi- 

 tion of the sands and gravels, it was still coursing through a 

 basin covered with drift, and this drift must certainly have 

 yielded its contributions to the river gravels, for by hypothesis 

 the conditions of drainage were such as to allow the rivers to 

 transport gravel and sand. The only escape from this conclu- 

 sion would be to suppose that neither the Mississippi nor its 

 tributaries north of the limit of drift, had power to transport 

 sand and gravel, or even silt, and that both the Mississippi and 

 its tributaries south of the drift limits, had such power. But 

 it is incredible that there could have been drainage conditions 

 up to within 25 miles of the edge of the ice, or up to within 

 25 miles of the drift sheet if the ice had retreated, such that 

 enormous quantities of gravel could have been brought in by 

 tributaries from right and left, and carried down by the Mis- 

 sissippi well toward the Gulf of Mexico, while the Mississippi 

 just above the point where current velocities necessary to the 

 above work existed, should be so sluggish as to bring down 

 nothing whatever of glacial gravel or sand or silt from the 

 north. If the main were strong enough to carry down the 

 gravel of its extra drift tributaries (and it certainly was, if the 

 Orange gravel be river gravel at all, or if it ever were trans- 

 ported through the Mississippi valley), it would in all likelihood 

 be strong enough to erode above these tributaries, and the 

 material wdiich it brought down from its intra-drift course, 

 would be admixed when deposited, with that contributed by 

 the extra-drift tributaries. If then the Orange gravels be 

 river gravels, and if drift existed in the Mississippi basin when 

 they were deposited, even if the ice had wholly retreated from 

 the same so that no glacial waters coursed through the valley, 

 such drift must certainly have yielded a contribution of gravel 

 and sand to the Mississippi, both directly and through tribu- 

 taries, at the same time that the tributaries south of the drift 



