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



volcanic breccia, composed of fine blackish grey sand, including small frag- 

 ments of clay slate and grauwacke five feet thick, rests upon loess, and is 

 covered by another deposit of loess fifteen feet thick, identical in composition 

 with the lower deposit. The flat surfaces of the slate and grauwacke frag- 

 ments, and numerous scales of mica, lie horizontal, producing a slaty structure, 

 and indicating their having assumed that position under the surface of water. 

 The schlucht, which opens towards the village of Lannesdorf, exhibits a 

 similar intermixture of scoriae in the loess, and it is about two miles and a half 

 distant from the crater of the Roderberg. — Thomae, 36—43. 



I shall now point out some of the more important observations of Mr. Lyell 

 on the loess in the higher parts of the Rhine valley and the adjacent country, 

 contained in the memoirs above mentioned, which throw light on the history 

 of this remarkable deposit. 



He observed it near Andernach, alternating with volcanic scoriae, &c., 

 and in one place '^covered with beds of pumice, trassy pumiceous sand, 

 and small dark volcanic cinders, forming upon the whole a mass from ten 

 to fifteen feet in thickness," — ejections from the neighbouring volcanos of 

 the Lower Eifel. In an excursion through part of the duchy of Darmstadt 

 by Mayence, Oppenheim, Alzey, Flonheim, Eppelsheim, and Worms, he 

 found the loess spread almost everywhere over the country. On the oppo- 

 site side of the Rhine, in the elevated table land above the Bergstrasse be- 

 tween Wiesloch and Bruchsal he observed the loess attaining a thickness of 

 200 feet. Near Strasburg large masses of it are seen at the foot of the 

 Vosges mountains on the left of the great plain of the Rhine, and at the base 

 of the mountains of the Black Forest on the other side. It occurs in con- 

 siderable force at Basle, and still higher up the Rhine at Waldshut, and 

 it is said to terminate between that place and Schaffhausen. In the hills 

 called Bruder Holz, about two miles south of Basle, it rests upon nearly 

 horizontal beds of molasse, and it has here an elevation of more than 1100 

 feet above the sea, which is more than 900 feet above that ridge of loess that 

 stretches between Bonn and Riingsdorf. In a section exposed at Bruder 

 Holz, he found the usual terrestrial and aquatic recent shells, and along 

 with them two vertebrae, which M. Agassiz says belong decidedly to a small 

 species of the Squalidae, or Shark family, perhaps to the genus Lamna. Mr. 

 Lyell has been so good as to allow me to have figures taken of these organic 

 remains, the first ichthyolites hitherto found in the loess and so remarkable in 

 a freshwater deposit*. 



* See Plate XXIX. 



