IOWA ACADEMY OP SCIENCE 
61 
At St. Joseph, Mo., the same structure may be observed along the ridge 
north of the Francis street depot of the C., B, & Q. R. R. Opposite to this point 
to the south and west, there are extensive mud and sand bars, the latter during 
dry seasons developing to some extent a dune structure at the surface. 
In the Indiana, Illinois and Missouri localities cited, this peculiar structure 
is shown only on the eastern side of the river. 
Hooper and West Point, Neb., west of the Missouri, are located near the east- 
ern extremity of an extensive sand dune area, a part of the famous sand-hill 
region of Nebraska. Exactly the same structure may be observed at both of 
these points and the relation of the loess to the sand is extremely suggestive 
of the aeolian origin of both deposits. 
Sometimes the sand grades upward into loess without interlamination, and 
the transition may then be explained as in the following section. 
(d). The gradual transition from loess to drift or sand, which may some- 
times be observed, especially where loess overlies the Kansan drift or the sands 
of the Iowan border, is also best explained on ecological grounds, though it has 
usually been considered evidence that the loess and drift form a practically un- 
broken series, and that the loess was deposited by ice or by glacial waters.* 
The fact should be emphasized that the extent of this intergradation has 
been greatly exaggerated. There is no general intermingling of drift and loess 
materials in irregular masses such as might be expected, at least locally, if 
water had promiscuously shifted these materials about in currents which varied 
in direction and force with the flood stage of the streams. On the contrary, 
when this transition does occur, and this is by no means the case in all places 
where loess and drift come in contact, it is quite consistently uniform and usu- 
ally complete within a vertical distance of two to six inches. There is no in- 
terlamination of materials other than that of sand and loess already noted, no 
coarse materials appearing in this relation in any of the numerous sections 
exmined by the writer. 
No cases are yet known in which drift materials appear in the loess, the 
one repeatedly cited in recent years by the advocates of the glacio-fluviatile 
hypothesis being an error in the determination of the lower member called 
loess. This is the supposed interloessial drift near Sioux City, Iowa, first re- 
ported by Todd and Bain** and later more fully described by the latter.*** It is 
a layer of boulder-bearing drift lying between what were reported to be two 
loesses. The writer has recently called attentiont to the fact that the lower so- 
called loess in this and similar exposures near Sioux City is a drift clay and not 
loess. This drift clay is common in the Missouri river valley and in some 
places attains a thickness of many feet, as is shown, for example, in the great 
Union Pacific railway cut-off in South Omaha, Neb., where it meets the loess 
without the interposition of a boulder-bearing stratum. 
While no interloessial drift, in the sense in which this expression was used, 
is known, interglacial loess-sheets are not uncommon, but they represent distinct 
* For example in the following and other papers : 
N. H. Winchell— 6th Ann. Rep. Geol. and Nat. Hist. Snr. of Minn., pp. 87-89, 1878; Bull. 
Geol. Soc. of Am., vol. 14, pp. 141-2, 1903; Am. Geol., vol. XXXI, pp. 279-282, 1903. 
W. J. McGee— nth An. Rep. U. S. Geol. Sur., pt. 1, 1891, pp. 442-7; etc. 
J. E. Todd-Proc. la. Acad. Sci., vol. XIII, p. 191, 1907. 
**Proc. la. Acad. Sci., vol. II, pp. 20-23, 1895. 
**’^Rep. Iowa Geol. Sur., vol. VIII, pp. 283-4, 1896. 
tProc. Iowa Acad. Sci., vol. XIV, 1908. 
