in wet, dark weather. I have taken large series from such places in Ohio 

 while on fossil collecting trips in rainy weather. Ledges of limestone, 

 especially if they are partly covered with soil, are fruitful collecting grounds 

 for snails. From the soil between two limestone ledges near Ottawa, I have 

 collected large numbers of Gastrocopta holzingeri, a snail that is otherwise 

 quite scarce in the area. Old quarries, overgrown with trees and shrubs, 

 are among my favorite collecting spots in Ohio and I have no doubt that 

 such situations elsewhere would be equally productive. Aurele La Rocque 



NON-MARINE PLEISTOCENE MOLLUSCA 



By Aurele La Rocque 

 Department of Geology, The Ohio State University 



The glaciers that covered large parts of Canada and the northern 

 United States several times in the last million years or so altered the 

 surface of the land wherever they spread. At this time, called Pleistocene 

 by geologists, deposits of fine, dust-like material, called loess, accumulated 

 in areas unaffected by the glaciers. As the glaciers melted, they poured 

 unusually large quantities of water into the river valleys and altered the 

 drainage pattern of the land, even far away from the glaciers themselves. 

 The land and freshwater mollusks that moved into the territory uncovered 

 by the melting glaciers give some indication of the history of the earth 

 during Pleistocene time. Careful collecting of Pleistocene Mollusca can be 

 of great scientific interest, yet it can be done without much special geologic 

 or biologic preparation. 



Pleistocene Mollusca are found in deposits of marl, where they are 

 probably commonest, loess, silts, and peaty material almost everywhere in 

 North America. Methods of collecting vary all the way from picking up 

 shells on the surface of a deposit, or taking haphazard samples of marl 

 from an exposure, to careful and systematic study of a particular deposit, 

 using all the resources of geologic and biologic techniques. The procedures 

 described here will yield material that can be used for scientific study of a 

 deposit. They can be varied according to the time and efTort the collector 

 is willing to devote to the work. Nevertheless, even grab samples have 

 their uses, especially in relatively remote areas, and the collector should 

 not give up the idea of collecting Pleistocene Mollusca because he has 

 neither the time nor the inclination to do the collecting in thorough fashion. 



In collecting, the first question is how much to collect. In some samples, 

 a handful of material will contain hundreds of shells, in others, only a few. 

 The first rule is to concentrate on getting a sample of the material with 

 shells, not on picking up individual shells on the surface. The second 

 question is how to pack the sample. Plastic bags, such as those used for 

 vegetables in grocery stores have been most satisfactory in the work done by 

 the writer and his students as they retain the moisture of the sample col- 

 lected. Some marls dry out as hard as rock if they are not washed and 

 sieved immediately after collecting and the shells arc then very hard to 



(70) 



