302 PREHISTORIC EUROPE. 



way down to lower levels. Meanwhile, what was once more or 

 less loose gravel had become cemented into hard pudding-stone. 

 Then came the last glacial epoch, when the glacier of the Ehone 

 re-advanced, and, grinding over the surface of the hardened 

 " alluvium," scratched and polished it, and eventually covered it 

 up with boulder-clay. 1 The ancient alluvium of the Bois de la 

 Batie is thus, in all probability, of the same age as the Diirnten 

 lignite and gravel beds. 



Some interestiug deposits recently discovered by Dr. Greppin, 

 near St. Jacob, in the Birsthal, not far from Basel, are believed 

 by Professor Heer to be likewise of interglacial age. The beds 

 consist of a considerable thickness of gravel and shingle (80 

 to 90 feet), with an interstratified layer of clay, over three feet 

 thick, which has yielded plant-remains, such as pine [Pinus 

 sylvcstris reflexa, Hr.), white birch, hazel, hornbeam, two willows 

 (Salix cinerea and S. atcrita, L.), cranberry, bog whortleberry, 

 bog-bean, privet, common dogwood, black alder, etc. — all the 

 species being still indigenous to the low grounds of Switzer- 

 land, and, with the exception of the bog whortleberry, to the 

 Birsthal. The same bed yields a few insects and many shells, 

 such as — 



Helix hispida. Succinea oblonga. 



„ arbustorum. Carychium minimum. 



„ pulchella. Clausilia parvula. 



„ crystallina. Pupa marginata. 



,, edentula. „ secale. 



„ montana. Limncea minuta. 



Planorbis vortex. Vitrina elongata. 



„ spirorbis. Cyclas fontinalis. 



„ carinatus. „ rivalis. 

 Physa hypnorum. 



From another bed of gravel in the same valley, which is a 

 continuation of the upper gravel-beds of St. Jacob, Dr. Greppin 



1 For descriptions of this interesting section see A. Favre, Bull. Soc. Geol. 

 France, 3 6 Ser. t. iii. p. 657 ; Ch. Lory, Ibid., p. 723 ; M. Tardy, Ibid., t. iv. 

 p. 182. 



