Mr. Horner on the Geology of the Environs of Bonn. 469 



have not been able to find anything more precise than that the loess at its 

 base contains portions of scoriaceous basalt, and that a mass of the same gravel 

 which covers the brown-coal formation, occurring at the edge of the crater, 

 lies under a dark volcanic tuff, or indurated mud. Dr. Hibbert states that in 

 the road from Andernach to Frauenkirchen he saw a section where a bed of 

 pumice, twenty-one feet thick, lies over a fine loess from forty-five to forty- 

 eight feet thick, and a coarser loess eighteen feet thick : he mentions other 

 places, which show that the volcanos in the Lower Eifel were in activity 

 subsequently to the deposit of the loess, and it is probable that this was 

 also the case of the Roderberg*. 



Of the relative Age of the Loess. 



This remarkable deposit, abounding in terrestrial and fluviatile shells of ex- 

 isting species, and containing in many places, some of which are more than 

 two hundred feet above the Rhine, bones of extinct species of the elephant 

 and rhinoceros, rests at Bonn, as it does at Strasburg, upon a deep mass of 

 that same gravel through which the Rhine flows in the greater part of its 

 course from Basle. It is the latest deposit found in this district prior to the 

 commencement of the recent period. 



It is difficult to conceive how it should have been produced, except by some 

 vast flood, which, if no elevations or subsidences of the land have since taken 

 place, must have been of the depth of at least six hundred feet, and several 

 miles in breadth, and so densely charged with mud as to leave behind, at an 

 elevation of two hundred feet, masses covering hundreds of acres, two hundred 

 and fifty miles distant from the spot where its first traces are to be seen, simi- 

 lar masses occurring at intervals not far asunder during the whole of that 

 course. That it was a sudden inundation, and that the loess was not gradually 

 and tranquifly deposited from stagnant water is probable, from there being no 

 signs of stratification, by its containing the remains of land and fluviatile shells, 

 and of land animals only, and by the great rarity of vegetable remains in it. 

 That plants and trees were not swept along by such a flood is extremely im- 

 probable; but they would obviously not sink in so dense a fluid, hurried along 

 with such a velocity as that with which it must have moved. Had there been 

 a gradual subsidence, not only would there have been stratification, but beds 

 of lacustrine and fluviatile shells, and abundance of leaves and other vegetable 

 remains. We must ascribe such a flood to the sudden bursting of the barrier 

 of a vast lake, the volume of water rushing over a great extent of land, and 



* See Appendix XI. p. 478. 

 3p 2 



