Mr. Horner ow the Geology of the Environs of Bonn. 481 



" lake of sufficient extent and depth to allow of the simultaneous accumulation 

 " of loess at all heights and throughout the whole area where it now occurs, I 

 " conceive that subsequently to the period when the countries now drained by 

 "the Rhine and its tributaries, acquired nearly their actual form and geogra- 

 " phical features, they were again depressed gradually by a movement like that 

 " now in progress on the west coast of Greenland. In proportion as the whole 

 " district was lowered, the general fall of the waters between the Alps and the 

 " ocean was lessened, and both the main and lateral valleys, becoming more 

 " subject to river inundations, were partially filled up with fluviatile silt con- 

 " taining land and freshwater shells. After this operation, when a thickness of 

 " many hundred feet of loess had been thrown down slowly, and in the course of 

 " many centuries, the whole region was once more upheaved gradually, but 

 " perhaps not equally, throughout the whole region. During this upward move- 

 '^ ment most of the fine loam was carried olFby denudation to such an extent that 

 " the original valleys were nearly re-excavated. The country was thus restored 

 " to its pristine state, with the exception of those patches of loess still remaining, 

 " and which, from their frequency and their remarkable homogeneousness of 

 " composition and fossils, attest the original continuity and common origin of 

 " the whole. By introducing such general fluctuations of relative level, we may 

 " dispense with the necessity of erecting and afterwards removing a great 

 ''barrier more than 1200 feet high, sufficient to exclude the ocean from the 

 " valley of the Rhine during the accumulation of the loess." 



Sweden has afforded the most unequivocal proofs that upward and down- 

 ward movements of the land may take place in countries where no ordinary 

 volcanic action is to be seen ; and that so gradually, as to be imperceptible to 

 all who are not watching the phaenomenon : and, as there are so many in- 

 dications of volcanic action in early times, on both sides of the Rhine valley, 

 it does not seem to me to be stretching theory beyond the limits of just phi- 

 losophical reasoning, to suppose that such oscillations may have taken place in 

 this district, during the gradual accumulation of the loess, and subsequently to 

 its deposition. 



END OF VOL. IV. 



