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



have been originally deposited. It has been shown that the great avidity 

 v^ith which it absorbs water, renders it liable to be easily washed away ; 

 and accordingly, wherever it is not protected by the form of the land, or by 

 a dense covering of vegetation, it is carried off by every shower ; and this 

 is in a great degree the cause of the yellow colour and the muddy state of 

 the Rhine after heavy rains. 



IX. Page 462. 

 In a gravel-pit near Bonn, I found a tooth of the Rhinoceros tichorinus. 

 The eravel is not that yellow alluvium which lies over the brown-coal forma- 

 tion, but resembles that of the present bed of the Rhine, and which I have 

 shown to be older than the loess. 



X. Page 468. 



Trachyte tuff is intermixed with the upper beds of the brown-coal forma- 

 tion in the lane between Nieder Bachem and Liessem, on the left bank of 

 the Rhine. — Thomae, p. 49, 



XI. Page 469. 



We have seen that from the volcanic focus of this district, limited though 

 it be in extent, products have been erupted which differ very much in their 

 nature, and that these different products must have been ejected at distinct 

 periods. The trachyte tuff appears to have been the first eruption, then 

 trachyte, then basalt, and lastly, the lava and scoriae of the Roderberg, which 

 resemble the ejections of the neighbouring Eifel, and partake very much of 

 the characters of those of active volcanos whose productions have more of an 

 augitic than a felspathic nature. 



That there was an eruption from the Roderberg subsequently to the com- 

 mencement of the deposit of the loesss, is proved by the thick beds of scoriae 

 which are incumbent upon loess near Lannesdorf ; and that it had become 

 extinct prior to the termination of that particular deposit is shown by beds of 

 loess covering the volcanic ejections, and still more conclusively by its accu- 

 mulation to so great a depth in the very bottom of the crater ; for had the 

 volcano been subsequently in activity, the loess must have been blown into 

 the air. That the edge of the crater must, in part at least, have been under 

 the surface of the water which transported the loess, is manifest, and that 

 collected at the bottom is probably the amount of the solid contents of the 

 fluid which filled the cavity. All the phaenomena seem to lead to the con- 

 clusion, that the Roderberg was a subaqueous eruption during the period of 



