EVIDENCE THAT BEDS AEE AFTONIAN 139 



molars and premolars of Eqmis scotti was found by Mr. Gladwin. (For 

 figure see ibid., plate 17.) 



22. Mad Creek section. — In this connection it may be of interest to 

 note the discovery of a fossiliferous bed of Aftonian in the eastern part of 

 the State of Iowa. This exposure is located on the east side of North Mad 

 Creek, in the northern part of Muscatine, Iowa, and was examined by the 

 writer in company with Professor Witter. Here a bed of typical Aftonian 

 sand and gravel (chiefly the former), about 25 feet in thickness, rests 

 unconformably on a bed of IsTebraskan drift and is separated from it by a 

 strongly oxidized ferruginous band. 



The greater part of the Aftonian consists of cross-bedded sand, but 

 near the top it contains a layer of gravel about 1 foot in thickness, from 

 which the late Professor F. M. Witter obtained a fragment of a molar of 

 Elephas primigenius. 



Overlying the Aftonian is an irregular, slightly pebbly, reddish layer 

 which is probably Loveland. It may, however, belong with the next 

 superimposed stratum, a reddish joint clay which closely resembles a late 

 or post-Illinoisan joint clay which is not uncommon in this vicinity. In 

 either case there is no doubt that the sands and gravels are Aftonian. 



Unidentifiable fragments of shells of mollusks were also found in the 

 sand. 



It will be seen that in the great majority of these fossiliferous sections 

 the silt, sand, and gravel beds are clearly below the Kansan, while in 

 several they are shown to be above the Nebraskan. Even in those cases 

 in which some of the members of the t3^pical section are wanting, the 

 sand and gravel beds occupy a consistent position with reference to the 

 members which are present. Moreover, it should be borne in mind that 

 throughout the territor^^ herein considered many more non-fossiliferous 

 exposures of similar beds occur, and that these, too, are uniformly con- 

 sistent with the fossiliferous beds in both structure and position. Again 

 and again the writer has seen non-fossiliferous beds of sand, gravel, and 

 silt lying unconformably between distinct Kansan and Nebraskan drift, 

 thus multiplying the evidence of stratigraphic position furnished by the 

 fossiliferous beds and leaving no doubt as to their horizon. 



Are THE Fossils Aftonian ? 



Some question may also arise as to whether the fossils really belong to 

 the Aftonian or were derived from other formations. Fossils from older 

 formations are sometimes found in the Aftonian, as they are in the 

 drifts, and a similar origin might be suggested for the fossils herein 

 discussed. 



