White on later Cretaceous deposits tn Iowa. 227 
or very near the place where they were found ; but even if they 
have been transported by drift agency, their original position 
must have been fully as far to the eastward as that in which 
they were discovered. 
The known position of the older Iowa formations, considered 
with reference to the land surface, seems to indicate that the 
maximum thickness of all the Cretaceous deposits which oc- 
curred within that state was much less than that which was 
reached by those formations further westward. But if we take 
into consideration the probable fact that those deposits wei'e 
exposed to the usual process of subaerial degradation during the 
whole of the Tertiary period; and that they were afterward 
exposed to glacial action, we readily perceive that a large part 
of the material originally deposited within the boundaries of 
Iowa may have been carried away. Still, the presence there of 
the later Cretaceous strata, indicates that the earlier ones have 
always had a comparatively small maximum thickness.^ 
After all the erosion which those strata have suffered, it is 
probable that at least in the northwestern counties of lowa^ 
there is still sufficient space between the drift deposit above and 
the paleozoic formations beneath, to allow of the presence there 
of several hundred feet in thickness of Cretaceous strata. We 
may therefore reasonably expect that the numerous excavations 
that will yet be made in that great drift-covered region, will 
result in the discovery there of some strata in situ. We may 
also expect to learn of many other discoveries similar to those 
of Hardin and Howard counties, in districts where small patches 
of Cretaceous strata have escaped destruction. 
' Just as this article is going to press I have received a note from the 
veteran paleobotanist, Prof. Lesquereux, concerning a leaf impression 
submitted to him, which was included in Prof. Haworth's collection. This 
form is unhesitatingly referred by Prof. Lesquereux to Andromeda 
parlatorii Heer, a characteristic species of the Dakota group. This may 
be taken as an indication that the earlier, as well as the later Cretaceous 
reached as far eastward as central Iowa. 
