Mr Lyell on the Loamy Deposit of the Rhine. Ill 



It may be as well to state, that the Loess consists of a pul- 

 verulent loam of a yellowish grey colour, containing a certain 

 quantity of carbonate of lime, according to Leonhard about a 

 sixth part. When not associated with gravel it exhibits no signs 

 of stratification. It contains almost everywhere imbedded ter- 

 restrial and aquatic shells of species still living in Europe, which 

 have usually lost their colour, but are for the most part entire. 



The Loess is found with its usual characters reposing here 

 and there upon the gravel of the plains of the Rhine at Bonn, 

 where I first examined it with attention, and patches of it are 

 seen of much greater thickness on the flanks of the Siebengebirge, 

 on the right bank, and at a corresponding height near the sum- 

 mit of the low hills which border the plain on the opposite bank. 

 In all these localities terrestrial shells, chiefly Helix and Pupa, 

 are by far the most abundant. 



I employed a collector for a fortnight in obtaining shells from 

 a deposit of Loess of considerable thickness, which is laid open 

 on the right bank of the Rhine about a mile and a half below 

 Bonn. The individual shells procured in an entire state amount- 

 ed to 217 in number, not a seventh part of which were of aquatic 

 species. The proportions were as follows : 



Terrestrial — Helix 167, Pupa and Clausilia 18; 185 individuals; AqtiaHc^-. 

 Lymnea 17, Paludina 10, Planorbis 5; 32 individuals; — 217. 



In order to compare these fossils with such shells as are now 

 drifted down by the Rhine, I made a collection of the latter at 

 low water from the mud and sand of the shore of the river for 

 several miles above and below Bonn. Along the beach is a line 

 of rubbish composed of small pieces of drift wood, leaves, weeds, 

 sand, and other matter, cast up principally by the large waves 

 raised by the steam-packets, as they cut through the water. Here 

 the greater number of drift shells occur, and I collected 273 in- 

 dividuals which were in the following'^proportions. 



Terrestrial Helix 133, Pupa and Clausilia 12, Bulimu8 2; 147 indi- 

 viduals; Aquatic — Paludina 48, Planorbis 34, Neritina 28, Lymnea 

 and Succinea 5, Unio 6, Ancylus 3, Cyclas 2 ; 126 individuals ;— 273. 



If I may be allowed to draw any general conclusion from this 

 comparison, it would appear that, in the waters of the Rhine, 



