VIII. — On the Geology of the Environs of Bonn. 

 By LEONARD HORNER, Esq., P.R.SS. L. & E., F.G.S. 



[Read March 13, 1833.*] 



X HE district about to be described lies on the Rhine, from the mouth of the 

 Sieg, below Bonn, to the town of Linz, a distance of about eighteen English 

 miles, and extends nearly five miles inland, on both sides of the river. 



A short way above Bonn the Rhine leaves the mountainous land, through 

 which it has flowed with little interruption from its source, and enters a vast 

 plain that extends to the North Sea, the nearest shore of which is about a 

 hundred and thirty miles distant. 



The SiEBENGEBiRGE, or Scveu Mountains, are the grand feature in the 

 district, and constitute a group of hills, of very graceful forms, on the right 

 bank of the river. Looking down from one of their higher summits, one sees 

 a numerous assemblage of conical hills and connecting ridges; but when 

 viewed from a distance, and in certain positions, seven peaks rise conspicu- 

 ously above the rest, and hence the group has received its name. Of these, 

 the most remarkable, as well from its individual form as from its fame in 

 legendary story, is the Drachenfels, with a ruined castle on its summit. But 

 the Oehlberg is the highest point, being 1369 English feet above the level of 

 the sea, or 1209 above the Rhine, the surface of which at Kbnigswinter, a 

 small town at the foot of the Drachenfels, is, at its mean height, 160 feet above 

 the seaf. (A table of the principal heights will be found in the AppendixX-) 



The Siebengebirge and adjacent country have been described with more or 

 less detail by several eminent geologists of Germany. The earliest memoir 

 on the volcanos of this district is probably that of " BARXiioLOMiEus Hempel- 

 MANN und JoH. WiLH. MuENSTER, Uebcrbleibscl erloschener Vulkane in 

 einigen Gegenden des Niederrheins." Bonn, 1785. There is a very copious 



* Between the reading and the printing of this paper, an interval of three years has elapsed, 

 and during that time some new facts have come to my knowledge, both from my own observations, 

 and from those of other geologists, which will be found in an Appendix, p. 472. — March, 1836. 



f By the barometrical measurements of Professor Benzenberg of Dusseldorf, in 1824. 



J Appendix I. p. 472. 



