Mr. Horner on the Geology of the Environs of Bonn. 479 



the loess, and that it was subsequently raised up gradually, en masse, into its 

 present position. 



XII. Page 470. 



The additional facts which have come to my knowledge since this paper 

 was read, the most important of which are narrated in the preceding notes, 

 have led me to modify in some degree the opinions I had formed relative to 

 the history of the loess. 



Its origin remains as uncertain as before ; but it is very evident that it 

 came from above Schaffhausen ; and as it is so uniform in its nature through- 

 out, with the exception of the somewhat redder tint of that at Dettelbach on 

 the Mayn, which may have been produced by some local intermixture, it is 

 fair to presume that it was derived from one source. 



Do its characters indicate that it was brought down by the water of the 

 Rhine, and was deposited gradually during a long period ; or, that it sub- 

 sided in a vast lake, into which the Rhine then entered, as the Rhone now 

 does into the lake of Geneva, and whose waters ran up into all those sinu- 

 osities of the land where remains of the deposit are still to be found } or, do 

 they point to the sudden rush of a muddy torrent, occasioned by the bursting 

 of a barrier which drained a vast lake, as I have already suggested ? 



The generally homogeneous unstratified nature of the loess, even though 

 in masses between 200 and 300 feet in thickness, always appeared to me to 

 be strongly presumptive evidence that it was deposited from a flood of water 

 densely loaded with mud, and moving with a velocity sufficient to transport its 

 solid contents to a distance so great as that from Basle to Bonn, before they 

 had time to fall to the bottom ; but the alternations of loess with gravel in the 

 valleys of the Neckar and the Lahn, and with volcanic ejections around An- 

 dernach, the Laacher See, and the Roderberg, show that, if it was a flood, 

 there must have been more than one. 



Were the idea of a lake at all admissible, there would be nothing extra- 

 vagant in supposing that the loess near Basle, which is more than 1100 

 feet above the level of the sea, and that of Bonn, which is less than 200 

 feet, might have been deposited in one and the same lake ; for it is only sup- 

 posing the water at the latter place to be 900 feet deep ; and the lake of Geneva, 

 according to Mr. De la Beche, is in some places 984*. But if the loess 

 were a gradual deposit from the waters of a lake, there would surely have 

 been indications of successive layers in the structure of the loess itself; the 

 shells would have been found more frequently in something like a similar 



* Manual, 3rd edit. p. 22. 



