IOWA ACADEMY OF SCIENCE 
243 
5. Where a distinct creeping of the loess has taken place ‘‘on 
steep slopes, when the lower portion has been rendered plastic by 
moisture,” the fossils in the deposit are as a rule, so badly crushed 
that it is impossible to secure perfect specimens even where fossils 
are abundant. The writer has observed shells thus crushed by 
evident creeping and slipping, at Natchez and Vicksburg, Miss.; 
Helena, Ark.; St. Joseph, Mo.; Council Bluffs and Missouri Valley, 
Iowa; Omaha, Neb., and other points. This creeping or faulting 
takes place chiefly, if not wholly, while the loess is moist, and 
when it is in that condition its fossils are as a rule soft and very 
frail, and hence easily crushed by the slightest movement of the 
bank. 
The perfection of the most delicate fossils in the great majority 
of fossiliferous exposures is sufficient proof that such movements 
have not been general. 
So far as concerns Professor Todd’s references to the occurrence 
of fossil localities on hillsides and near streams; to the presence 
of non-fossiliferous exposures “in apparently equally favorable lo- 
cations,” and of their occurrence at points remote from streams, 
they are wholly irrelevant. 
The variations in distribution have been discussed by the writer,* 
who has repeatedly pointed out the striking similarity in the 
distribution of modern and fossil forms in various localities. Stu- 
dents interested in these problems, who will go to the field and care- 
fully compare the distribution of both living and fossil forms, 
will be convinced of this similarity, and will appreciate the fact 
that it is evidently caused by like conditions,— conditions such as 
now prevail over the same area. 
The inequality of distribution of the fossils which has so at- 
tracted Professor Todd’s attention, is exactly duplicated by the 
modern forms. A grove, remote from a stream or adjoining it, 
may have many living mollusks, while another, in either situation 
and seemingly similarly placed, may have none. Prairie areas, 
wholly without woody plants, will have few or no living mollusks, 
and as the greater part of the territory remote from streams 
throughout the Mississippi valley is prairie, its molluscan fauna 
is limited and local. 
Similar conditions in all probability prevailed during the forma- 
tion of the several loesses (one following each glacial drift), and 
*See especially Proc. Ia. Acad. Sci., Vol. VI, pp. 98-111, 1899, or Journal of Geol., Vol. 
VII, pp. 122-136, 1899. 
