282 PREHISTORIC EUROPE. 



also occurs, together with many more or less comminuted frag- 

 ments, some of which appear to belong to Cyprina islandica. 

 Entire specimens of these shells have not yet been found, all, 

 with the exception only of Yoldia, being crushed and broken. 

 That the clay in which they occur has experienced enormous 

 pressure is shown, says Penck, by the extraordinary confusion 

 and disturbance of its bedding. In fact it has been so firmly 

 compressed and squeezed, and is now so hard that at the tileries 

 they blast it with gunpowder. 



Freshwater beds of sand with Dreissena sp. and Valvata sp. 

 were detected by Penck in association with this Yoldia clay. 

 They were characterised by the presence of small fragments of 

 northern rocks, such as bits of Silurian from Gottland, and 

 fragments of felspathic and crystalline rocks. These he thinks 

 could only have been derived from some pre-existing mass of 

 boulder-clay in Germany — probably on the same horizon as that 

 of the third or lowest boulder-clay of Mark Brandenburg. 



Passing south into Saxony we find that the upper boulder- 

 clay of Prussia and North Germany is wanting, the two boulder- 

 clays which do occur corresponding to the second and third 

 boulder-clays of Mark Brandenburg. The succession of deposits 

 given by Penck is as follows : 



Drift-Formation or Saxony. 



1. Upper boulder-clay, containing isolated sporadic specimens of Paludina 



diluviana. This bed corresponds to the second 

 boulder-clay of Mark Brandenburg. 



2. Flood- and River- 



gravel and sand. — On same horizon as the freshwater interglacial 

 beds of Potsdam, and the marine stoneless clay 

 of Elbing, near the Frisches Haff. 



3. Lower boulder-clay, representing the third or lowest boulder-clay of 



Mark Brandenburg. 



4. Sand with northern 



materials . . . Corresponding to the sand and northern materials 

 which underlie the lowest boulder-clay of Mark 

 Brandenburg. 



One of the most interesting points in connection with the drift- 



