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



of lignite were worked, separated from each other by clay and friable sandstone *. The Menden- 

 berg is 1198 feet above the Rhine, and the lignite beds occur within 300 feet of the summit. 



Loess. 



■ The substance to which this name is applied is a sandy calcareous loam of 

 a yellowish brown colour^ slightly coherent, and absorbing water with great 

 avidity. It is a deposit which has been generally considered to be peculiar to 

 the Rhine valley f, and it is found, to a great extent, at detached points on 

 both sides of the river, from Basle to Bonn. It has not been noticed by pre- 

 vious writers on the district described in this paper with that attention to which 

 its geological importance entitles it. Loess is specially noticed by Leonhard 

 in his Charakteristik der Felsarten, published in 1824, who has adopted this 

 trivial name, given to it in the neighbourhood of Basle %; but a fuller account 

 of it has more recently been given by Professor Bronn§, in his description 

 of the environs of Heidelberg, and from which I have put together the fol- 

 lowing particulars. 



It is found on the sides of the hills next the Rhine valley, and penetrating into the side valleys, 

 such as that of the Neckar, Mayn and Lahn, and occurs chiefly in those situations where the form 

 of the land presented a barrier against its being washed away by a descending stream. It is, for 

 example, more abundant near Worms and Oppenheim than near Heidelberg, because the force 

 of the Rhine is chiefly directed there against its right bank. It is found at various distances from 

 the plain of the Rhine, as much as nine miles, and it is in some places 600 feet above the level of 

 the sea. 



One hundred parts of that near Heidelberg yielded 50 per cent, of siliceous sand, 16^ of 



* Von Oeynhausen and Von Dechen in Hertha, vol. xii. 1828. 



t In the synopsis of the successive deposits in the basin of Vienna, given by Mr. Murchison, 

 the uppermost is described to be " Alluvial loam, called Loss, with terrestrial shells of existing 

 *' species, (of the genera Pupa, Helix, and Succinea,) mixed with bones of elephants of extinct spe- 

 " cies. The average thickness of this deposit is about 60 feet, but at some places the thickness is 

 " much greater." Further, "It is greatly expanded near Krems and St. Polten, reaching occasion- 

 " ally the thickness of 140 feet, and having, near these places, the exact appearance of the old allu- 

 " vial hillocks in the valley of the Rhine, which have been described by M. Voltz." — Geological 

 Transactions, vol. iii. pp. 402, 405. 



Loess is said to occur also in the valleys of the Garonne and the AUier. — Rozet, Journal de 

 Geologic, i. 57. 



;{; It is mentioned by the name of Brits by Steininger in his Neue Beiirdge zur Geschichte der 

 Rh.einischen Vulkane. 1821. 8vo. 



V § G(sa Heidelbergcnsis, oder Mineralogische Beschreibung der Gegend von Heidelberg. 1830. 

 See also Voltz, Uebersicht der Mineralogie der beiden Rhein-Departemente ; and Rozet, Sur le 

 Diluvium de la Vallee du Rhin, in Journal de Geologic, vol. i. 



