Mr. Horner on the Geology of the Environs of Bonn. 477 



Ascending the valley of the Neckar, he found a section near the Manheim 

 gate of Heidelberg, exhibiting alternating layers of loess and gravel, to the 

 thickness of 12 feet. He saw it near Heilbronn at an elevation of 500 feet 

 above the level of the sea, and was informed that it lies on the hills in that 

 neighbourhood, 300 feet higher. Further up the Neckar, at Canstadt, near 

 Stutgardt, it overlies a freshwater formation of tuff travertine and marl, and 

 south-east of Stutgardt, between Goppingen and the little watering-place of 

 Boll, he found it in a valley watered by a small tributary of the Neckar. 

 From Goppingen his route lay eastward by Weisenstein and Heidenheim to 

 Nordlingen, and between Weisenstein and Heidenheim he crossed elevated 

 land, on the west side of which the waters flow to the Rhine, on the east to 

 the Danube, and eastward of this ridge no more loess was to be seen. 



Returning again to the tributaries of the Rhine, in proceeding westward 

 from Bamberg in Bavaria, he found the loess at Dettelbach, a small town on 

 the Mayn, eastward of Wiirtzburg ; and not only in the valley, but on the 

 neighbouring hills of muschelkalk, at a height of five or six hundred feet 

 above the valley. It was here of a somewhat redder tint than in Wiirtem- 

 berg, and Mr. Lyell conjectures that the colouring-matter may have been 

 derived from the neighbouring red bunter-sandstein. Lower down the 

 Mayn, he again saw the loess at Hochst below Frankfurt, and at Soden, 

 where it abuts against the elevated grauwacke ridge of the Taunus. 



Crossing the Taunus to the valley of the Lahn, he again found the loess at 

 the village of Elz near Limburg. "On the north of this village," he says, 

 " is a hill, which forms one boundary of the valley of the Lahn, and here 

 loess is seen with all its usual characters, with many land and freshwater 

 shells, and alternating, as at Heidelberg, with gravel. I observed, in par- 

 ticular, a horizontal layer of white quartz pebbles, a foot and a half in thick- 

 ness, resting on a mass of loess fifteen feet thick, and covered by loess five feet 

 in thickness, the loess, in both situations, including in it entire shells. Follow- 

 ing the road, I found the slope of the hill above to consist of horizontal beds 

 of quartz pebbles, which have a base of loess. Hence it appears that the valley 

 of the Lahn, which is excavated through highly inclined greywacke, has, at 

 some period since its excavation, been partially filled up with beds of gravel al- 

 ternating with loess, a great part of which has since been removed by de- 

 nudation." 



It is material to observe that all the above-mentioned places, where Mr. 

 Lyell observed the loess, have a direct communication with the main valley 

 of the Rhine ; that is, form part of one hydrographical basin. The quantity 

 left bears but a small proportion to the mass which we must suppose to 



3 q2 



