Mr Lyell on the Loamy Deposit of the Rhine, 119 



of the Rhine, a yellow argillaceous and sandy rock, is very ge- 

 nerally concealed under a deep covering of loam, which appears 

 to have resulted from the decomposition of this greywacke, and 

 not to have been transported from any distance. This loam has 

 precisely the ordinary colour of the loess, and contains a great 

 quantity of quartz pebbles. 



The same alluvium is very genera 1 in the Westerwald, espe- 

 cially on the surface of that high table-land around Altenkirchen, 

 Uckerath, and between that place and Siegburg, a district lying 

 immediately behind the Siebengebirge. 



No. 3. 



a a Loess with shells. h b Beds of quartz pebbles. 



The principal river which intersects the table-land of Nassau 

 is the Lahn, which I crossed at Limburg, about twenty miles 

 above its junction with the Rhine. The road from Limburg to 

 Freilingen passes first by Elz. On the north of this village 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 fresh-water shells; and alternating, as at Heidelberg, 

 with gravel. I observed, in particular, a horizontal layer of 

 white quartz peebles, a foot and a half in thickness, resting on 

 a mass of loess fifteen feet thick, and covered by another bed of 

 loess five feet in thickness ; the loess, in both situations, includ- 

 ing in it entire shells. Following 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 

 thq Lahn, which is excavated through highly inclined grey« 

 wacke, has, at some period since its excavation, been partially 

 filled up with beds of gravel, alternating with loess, a great part 

 of which has since been removed by denudation. (See Section, 

 No. 3.) It appears that, during the accumulation of the mass, 

 fine loam was sometimes thrown down, containing unbroken 

 shells, then gravel, and then again the shelly loam. 



On a review of the observations above mentioned, it appears 



