ON THE PLOBOSCIDEAN FOSSILS OF THE PLEISTOCENE DEPOSITS. 51 



originally belongiiig to the alluvium from which they came. I'i- 

 nally, several teeth have been found in gravels, whose age iw 

 unknown, and in which they are evidently inbedded secondarily. 

 It appears that about one half the number of all. the fossils re- 

 corded cannot be assigned to any particular relation to the drift 

 on the evidence of the original record. 



Mastodon remains are reported in one case as coming from 

 the "Kansan drift or immediately below this drift". This find 

 was made in a well on the poor-farm at Mount Pleasant, in Iowa. 

 Coming from such an excavation, circumstances seem to have 

 been favorable for exact determination of the horizon. There were 

 several teeth and bones, and this makes it reasonably certain that 

 the bones were in situ. In all likelihood the animal lived, perished, 

 and was buried on the land in eastern Iowa before the advance 

 of the ice which brought the Kansan drift. Fossils in a till can 

 hardly be regarded as in situ. They would be ground to pieces 

 by the ice. 



Parts of skeletons of the mastodon have been found in some- 

 what similar positions on the upper surface of the Kansan drift, 

 in the so-called "ferretto zone". This is the old and weathered 

 land surface which developed after the Kansan drift had been de- 

 posited. This drift is now covered by loess, but in some localities 

 it has been almost entirely removed. Under thirty feet of loess, 

 which rested on two or three feet of drift, a mastodon jaw with 

 two teeth was found near Alton, in Illinois. In Washington 

 county, in the same state, other mastodon remains are recorded 

 as having come from the same horizon, one from near Sandoval, 

 and another from near Beaucoup. Some teeth, a tusk, and some 

 bones of a mastodon were recently found "in the upper part of the 

 till, under the loess", near Akron, in Plymouth county, in Iowa. 

 This till is also believed to belong to the Kansan. 



The ''ferretto zone" is to be seen under the loess only beyond 

 the borders of the drift sheets which are later than the Ulinoian. 

 Fossils from this zone must be 3'ounger than the Kansan drift 



