214 Dana and Chambers on Ancient Sea- Margins. 



If the last elevation of sixty feet (or thirty, if it be so) which 

 Scotland has experienced, produced elevated sea-beaches, and 

 no proper river terraces, — if all the existing river terraces 

 are remains of other sea-beaches, and proofs of other higher 

 elevations, — then another elevation of sixty feet would pro- 

 duce a similar result, and this alone. In order to ascertain 

 the truth, the necessary effects of such a change of level may 

 be briefly reviewed. These effects are as follows ; — 



1. The formation of elevated beaches, on many parts of the 

 sea-coast, about sixty feet above the sea, varying in height 

 somewhat, as actual sea-shores vary, according to their posi- 

 tion with reference to the winds and tides. 



2. The beds of rivers being raised, as well as the rest of 

 the land, the amount of descent to the sea would be in- 

 creased ; and, in consequence of this, their waters would 

 run more violently, the excavating force would be augmented, 

 and they would go on with a process of rapid degradation, 

 until the former rate of descent was reached. Towards the 

 mouths of the streams, the bed might be deepened the whole 

 sixty feet. Above, the amount would vary for any given 

 period, according to the ability of the waters in different 

 parts to wear out the material over which they pass. A hard 

 rocky bed might prevent excavation; and, if the material 

 were yielding above such a place, the wear might there level 

 down the surface, and produce a range of slow waters, end- 

 ing in rapids over the harder unyielding rocks. The amount 

 of excavation might thus vary from sixty feet, the maximum 

 depth, to only a few feet along the tributaries. 



3. Besides depressing their beds, the rivers would act la- 

 terally, and carry off the alluvium of their banks (when any 

 existed), and every flood would aid in this result, until finally 

 a broad flat, or " bottom-land," in many places bordered the 

 streams. Such a flat, situated within the reach of the river 

 floods, is common on parts of all rivers where their descent 

 is not too rapid. The breadth of the flat would depend on 

 the amount and force of the waters during floods, and it 

 would necessarily be bounded by a steep slope rising to an 

 upper level. Where the valley was narrow, all the former 



