332 LOESS IN BASINS OF THE NECKAK AND DANUBE. CHAP. xvi. 



Dr. Falconer. At this place the loess is covered by a thick 

 bed of travertin, used as a building stone, the product of a 

 mineral spring. In the travertin are many fossil plants, all 

 recent except two, an oak and poplar, the leaves of which 

 Professor Heer has not been able to identify with any known 

 species. 



Below the loess of Canstadt, in which bones of the mam 

 moth are so abundant, is a bed of gravel, evidently an old 

 river channel, now many feet above the level of the Neckar, 

 the valley having there been excavated to some depth below 

 its ancient channel so as to lie in the underlying red sand 

 stone or keuper. Although the loess, when traced from the 

 valley of the Rhine into that of the Neckar, or into any 

 other of its tributaries, often undergoes some slight alteration 

 in its character, yet there is so much identity of composition 

 as to suggest the idea, that the mud of the main river passed 

 far up the tributary valleys, just as that of the Mississippi, 

 during floods, flows far up the Ohio, carrying its mud with it 

 into the basin of that river. But the uniformity of colour 

 and mineral composition does not extend indefinitely into 

 the higher parts of every basin. In that of the Neckar, for 

 example, near Tubingen, I , found the fluviatile loam or 

 brick-earth, enclosing the usual helices and succinese, to 

 gether with the bones of the mammoth, very distinct in 

 colour and composition from ordinary Rhenish loess, and 

 such as no one could confound with Alpine mud. It is 

 mottled with red and green, like the New Red Sandstone or 

 keuper, from which it has clearly been derived. 



Such examples, however, merely show that where a basin 

 is so limited in size that the detritus is derived chiefly, or 

 exclusively, from one formation, the prevailing rock will 

 impart its colour and composition in a very decided manner 

 to the loam ; whereas, in the basin of a great river which has 

 many tributaries, the loam will consist of a mixture of 



