278 PREHISTORIC EUROPE. 



freshened by the influx of water (streams and rivers) from the 

 land. 



It is to be noted that most of the shells that occur in the 

 German till are, according to Penck, so broken and abraded 

 that the species is often difficult to determine ; and Berendt 

 has figured a specimen of Cardmm edule which is distinctly 

 striated. Penck found a similar specimen in the boulder-clay 

 of Marienburg in West Prussia, and the geological collection 

 in the University of Breslau, he says, contains another. The 

 same geologist mentions another noteworthy fact ; the shells are 

 sometimes filled with a material differing entirely from that of 

 the till in which they lie embedded. Thus a specimen of 

 Paludina diluviana in the coarse boulder-clay of Eixdorf, which 

 lies a few miles east of Berlin, was filled with a fine ductile 

 clay, and a JVassa reticulata from the boulder-clay of Dirshau 

 in West Prussia, with fine sea-sand. It is evident, indeed, 

 that all these sporadic specimens of molluscs are merely 

 erratics like the glaciated stones amongst which they occur. 

 They have been derived from some pre-existing beds which 

 the mer de glace has demolished and commingled with its 

 bottom -moraine. The question now arises whether we can 

 tell anything about the history of those beds which have thus 

 been so highly broken up and destroyed. Were they of pre- 

 glacial or interglacial age ? Fortunately some portions have 

 been preserved, the position of which, intercalated between 

 two distinct sheets of boulder-clay, settles at once their inter- 

 glacial age. 



On the valley-slopes of the Spree, in the neighbourhood of 

 Eixdorf, there is a line of sandpits in which the following sec- 

 tion is laid bare : — 



1. Upper boulder clay . . . 6 to 10 feet. 



2. Sand, with gravel and rolled stones in under 



portion . . . 30 „ 40 „ 



3. Lower boulder clay . . .10 „ 



4. Sand. 



Prom the sand (No. 2) many remains of the Pleistocene 



