Mr I-.yell on the Loamy Deposit of the Rhine. 121 



of every age along the borders of the great plain of the Rhine, 

 and we naturally incline at first to suppose that a vast lake has 

 existed, of which the barrier may have been somewhere near 

 Bingen, formed by the union of the mountains of the Hundsruck 

 and Taunus, before the deep and picturesque gorge of the 

 Rhine, between Bingen and Bonn, had been opened, or occa- 

 sioned by the choking up of that gorge by lava or ejections from 

 the volcanoes bordering the Rhine below Bingen. Of this lake, 

 the valleys of the Neckar and the Mayn would have formed 

 two great bays. According to this hypothesis, the depth of 

 water must have been sufficient to have allowed a loamy sediment 

 to be thrown down not only on the gravel of the Rhine, but at 

 the height of 600 feet or more above that level, on the boundary 

 heights. Afterwards, we must suppose that an opening was 

 made through the barrier, and the lacustrine sediment denuded, 

 until at length the original valleys of the Rhine and its tributa- 

 ries were re-excavated, and small patches only of loess left here 

 and there. 



But this explanation is not sufficient, for when we pass from 

 Bingen to the country of Neuwied, we find masses of the same 

 loess rising to considerable heights above the Rhine, so that we 

 require another lake, or we must remove the barrier of the great 

 lake farther down than Andernach, If we then suppose it to 

 have been in some of the narrowest parts of the great gorge be- 

 tween Andernach and Bonn, we again encounter a similar ob- 

 jection ; for, on examining the Siebengebirge, we discover the 

 loess at great heights on its flanks, as also on the opposite hills 

 behind Poppelsdorf; and we are then under the necessity of con- 

 structing an imaginary dam, many hundred feet in height, which 

 should stretch across a wide part of the plain below Cologne. 

 Even if we are prepared to assume the former existence of one 

 or more such barriers, we have still to assign adequate causes 

 for their removal. 



It is clear that no theory can account for the position of the 

 loess, which does not admit great revolutions in the physical 

 geography of the country now drained by the Rhine and its 

 tributaries, within a very modern geological period, when all 

 the existing testacca inhabited the country. 



It seems also indispensable to assume that some barriers have 



