THE NAUTILUS. 65 



Polygyra mflecta, Helicodiscus parallelus, 



Polygera fraterna, Catnpeloma subsolidum, 



Polygyra monodon, Pleurocera sp. ? , 



Polygyra hirsuta, Sphaerium transversum. 



The second locality examined was an exposure of typical loess 

 in the government quarry a short distance above the town of 

 Mokane on the M. K. & T. R. R. The full section of strata 

 exposed in the quarry face measures approximately seventy 

 feet ; rising abruptly from the flood-plain of the river, the Jeffer- 

 son City formation (Ordovician) presents a precipitous face of 

 sixty feet followed by a layer of tough, bluish clay, interspersed 

 with worn fragments of limestone ; upon this bed of clay is 

 deposited a layer of loess that varies in thickness but having 

 probably an average of nine feet. The loess is capped with a 

 layer of soil rich in humus and supports a flora typical of the 

 Missouri Bluff region. 



While occasional specimens of the species listed were found 

 throughout the entire thickness of the loess, it was only in a 

 thin zone, about sixteen inches from the base, that they were 

 collected in abundance, in fact they are so abundant in this zone 

 as to attract attention from the highway below, by the white 

 line they present at the top of the quarry, being even more pro- 

 nounced than the Ordovician-Pleistocene contact. 



Of the entire series collected from this exposure, all have lost 

 their color markings and uniformly present the usual chalky 

 appearance common to the fossils of the loess. 



A few are filled with a heavy iron-stained deposit ; others are 

 filled with the surrounding loess mass and occasionally speci- 

 mens are unfilled and crumble to dust upon their removal from 

 the matrix. 



Careful examination of all fragmentary as well as the better 

 preserved shells in the collection gathered at this place fails to 

 detect a single aquatic species, the fauna being composed wholly 

 of land forms, and their being massed together in a single layer 

 can be readily explained as an accumulation left in a depression 

 after a torrential rain. However, a misinterpretation of condi- 

 tions, such as presented in this locality, combined with a lack 

 of knowledge of the habits of the forms found, has led a number 



