CHAP. XVI. THE LOESS IN BELGIUM. 331 



derived from the disintegration of the crystalline rock, which 

 must have decomposed in the atmosphere before the mud 

 had reached this height. Entire shells of Helix, Pupa, and 

 Succinea, of the usual living species, are imbedded in the 

 granitic mixture. We may therefore be sure that the valley 

 bounded b}^ steep hills of granite existed before the tranquil 

 accumulation of this vast body of loess. 



During the re-excavation of the basin of the Ehine, suc- 

 cessive deposits of loess of newer origin were formed at 

 various heights ; and it is often difficult to distinguish their 

 relative ages, esj^ecially as fossils are often entirely wanting, 

 and the mineral composition of the formation is so uniform. 



The loess in Belgium is variable in thickness, usually 

 ranging from ten to thirty feet. It caps some of the highest 

 hills or table-land around Brussels at the height of 300 feet 

 above the sea. In such places it usually rests on gravel, and 

 rarely contains shells, but when they occur they are of recent 

 species. I found the Succinea oblonga, before mentioned, 

 p. 327, and Helix hisj^ida, in the Belgian loess at ISTeerepen, 

 between Tongres and Hasselt, where M. Bosquet had pre- 

 viousl}^ obtained remains of an elephant referred to E. primi- 

 genius. This pachyderm and Rhinoceros tichorhinus are cited 

 as characterizing the loess in various parts of the valley of 

 the Ehine. Several perfect skeletons of the marmot have 

 been disinterred from the loess of Aix-la-Chapelle. But much 

 remains to be done in determining the species of mammalia 

 of this formation, and the relative altitudes above the valley- 

 plain at which they occur. 



If we ascend the basin of the Neckai*, we find that it is 

 filled with loess of great thickness, far above its junction with 

 the Rhine. At Canstadt near Stuttgart, loess resembling 

 that of the Ehine contains many fossil bones, especially those 

 of Elephas primigenius, together with some of Rhinoceros 

 tichorhinus, the species having been lately determined by 



