Mr. Horner on the Geology of the Environs of Bonn, 475 



sediment obtained from a large quantity of the water has the same appearance^ 

 and is of the same composition as loess. 



In the Edinburgh Philosophical Journal for July 1834^ there is a paper by 

 Mr. Lyell on this peculiar deposit: he has treated of it very fully in his 

 " Principles of Geology/* vol. iv. p. 44, 4th edition ; he read some addi- 

 tional observations upon it at the Geological Society in December 1835, an 

 account of w^hich is given in the Society's " Proceedings/' vol. ii. p. 221, and 

 he again refers to it in his Address at the Anniversary of the Geological Society, 

 in February, 1836. M.Thomae, in the w^ork above cited, has recorded several 

 interesting facts respecting the loess w^hich lies around the Roderberg. We 

 learn, from the observations of these gentlemen, the follow^ing particulars in 

 addition to those mentioned in my paper. 



Of the shells found in the loess near Bonn the terrestrial predominate 

 greatly over the aquatic ; the same rule holds good, though not to the same 

 extent, with respect to the shells now drifted down by the Rhine, and con- 

 tained in the mud and sand of its shores ; and the greater proportion of these 

 last agree specifically with those buried in the loess. — Lyell, Memoir of 1834^, 



P-3. 



The loess absorbs water with great avidity, and where exposed to the action 

 of water is often carried away in great masses. It affords a very fertile soil ; 

 but the husbandman is sometimes doomed to see his hopes blasted by a violent 

 storm of rain washing away the whole soil from his field, laying the roots of 

 his vines bare to the sun. — Thomae, 26. 



On the east side of the Roderberg there are five round-back ridges, co- 

 vered with vegetation, which seem to radiate from the lower part of the hill 

 towards its base. These are composed of loess ; and, at their inferior ex- 

 tremity, are in some places laid open, exhibiting a vertical section from twenty 

 to thirty-five feet in height, resting upon a mass of gravel, identical in com- 

 position with that forming the present bed of the Rhine, and from four to eight 

 feet in thickness. — Thomae, 29 — 31. 



" On the north-north-west side of the Roderberg a valley separates the 

 volcano from the Zilliger Haidchen, heathy hilly ground composed of loess, 

 which is furrowed in several places to a great depth. These excavations are 

 called in German schluchten, meaning hollow ways. In some of these the loess 

 is seen to be intermixed with volcanic products, and containing detached ac- 

 cumulations of scoriae in amorphous masses. In several places there are con- 

 tinuous beds of scorifB lying upon and covered by loess. In one of the 

 schluchten a section is exposed, exhibiting alternate layers of scoriae and tuff, 

 resting on the fundamental grauwacke, and covered by loess ; in another a 



VOL. IV.— SECOND SERIES. 3 Q 



