266 LECTURE X. 



feet thick of coarse^ wliite^ chalky sand, with flints but little 

 rolled, about three inches in diameter, intermixed with many- 

 flint balls, washed forth unbroken from the chalk, and forming 

 a confused bed in which layers of fine sand alternate with sandy 

 marl. In the fine sandy layers are frequently found sea- and 

 fresh- water shells still existing in the district, excepting a spe- 

 cies fCyrena fluminalis) , which at present is only met with in 

 the Nile and some parts of High Asia, namely in Cashmir. 

 Here and there the fresh water shells are intermixed with the 

 strand mussels of the sea which still live in a neighbouring 

 canal, showing that the sea made frequent irruptions far into 

 the land. Besides this, there are found in this inferior bed of 

 the lower terrace, in immediate contact with the chalk soil, 

 fossil bones, and, associated with them, flint implements, of 

 which more anon. The bones found in this bed are generally 

 those of the mammoth, the rhinoceros with a bony septum, the 

 fossil horse, the aurochs, the gigantic deer, the reindeer, the 

 cave lion, the cave hy^na, and other extinct cave beasts. 



This older stratum generally presents an irregular surface, 

 with eminences and depressions, as seen in all beds deposited 

 by the irregular flow of the waters. Above it lies fine white 

 silicious sand, with rounded pebbles and thin beds of marl, in 

 which also here and there some fragments of the bones of ex- 

 tinct animals are met with. This bed has manifestly been 

 deposited at a later period ; it has a mean thickness of six feet, 

 and contains no other petrifactions. 



Upon this lies a bed of brown clay, mixed with a few angu- 

 lar flints, filling up the depressions in the surface of the second 

 bed, and passing here and there into an ochrous sand which 

 contains no fossils. The surface is even, and covered with a 

 layer of common earth of considerable thickness. Old graves 

 occasionally found in this terrace sometimes pass through the 

 superior brown clay bed to the white sand bed, but never reach 

 its bottom. They are known at once, being filled with brown 

 earth and human bones. 



The upper terrace is similarly constructed, so that it is not 

 easy to point out any difierence. 



The central parts of the valleys are generally filled with peat 



