1 74 Natural, History Bulletin. 



gish currents at lower water, and we find a .consequent 

 mingling of coarse and fine material, as well as of the shells 

 deposited under somewhat different conditions in the strata a 

 and c. The uppermost stratum, a^ consists of very fine allu- 

 vium, rich in carbonaceous matter, and containing some fossils 

 belonging to genera which live on land, or in ponds and 

 shallow, sluggish waters. 



This was evidently deposited during over-flovv's by the 

 stream which had previously receded from the old sand-bars 

 and flats now represented by h and c. During floods the 

 water, laden with fine silt, spread, or backed up, over the low^- 

 lands on which it entrapped the mollusks which lived upon 

 the land, or in the shallow ponds, in a deposit of fine alluvium. 

 Very few shells other than those which occur in such habitats 

 are found in this deposit, and their similarity to the shells of 

 the Loess formation is striking. Is it not probable that a con- 

 siderable portion of our Loess was deposited under similar 

 conditions, which however were more favorable on the whole 

 to the deposition of larger quantities of fine silt, the country 

 being less eroded and hence less broken and the rivers receiv- 

 ing more water and spreading out over larger areas ? 



Like the stratum a the Loess consists of fine material which 

 is usually luistratificd and tmUnninated. The fossils of the two 

 deposits are nearly the same. The difference in color is very 

 marked, a being black and the Loess, a hght yellow, but is it 

 not extremely probable that the carbonaceous matter, which 

 once probably formed an equally marked constituent of the 

 Loess, was consumed in the deposition of ferric oxide which 

 occurs in spots, streaks, and bands in all of the fossiliferous 

 portions of the deposit ? 



The similarity of these two deposits is certainly striking. 



