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Updated: June 27, 2025
The level of certain parts of the bed of the river referred to by Lombardini as constant, is not their elevation as compared with points nearer the sea, but relatively to the adjacent plains, and there is every reason to believe that the depression of the Adriatic coast, whether, as is conceivable, occasioned by the mere weight of the fluviatile deposits or by more general geological causes, has increased the slope of the bed of the river between the points in question and the sea.
The evidence obtained by naturalists that some of the extinct mammalia of Menchecourt really lived and died in this part of France, at the time of the embedding of the flint tools in fluviatile strata, is most satisfactory; and not the less so for having been put on record long before any suspicion was entertained that works of art would ever be detected in the same beds.
The name of Wealden was given to this group because it was first studied in parts of Kent, Surrey, and Sussex, called the Weald; and we are indebted to Dr. Mantell for having shown, in 1822, in his "Geology of Sussex," that the whole group was of fluviatile origin.
In these cases we as frequently find fresh-water beds below a marine set or shallow-water under those of deep-sea origin as the reverse. Thus, if we bore an artesian well below London, we pass through a marine clay, and there reach, at the depth of several hundred feet, a shallow-water and fluviatile sand, beneath which comes the white chalk originally formed in a deep sea.
Peat, 20 to 30 feet thick, resting on gravel, a. 2. Lower level gravel with elephants' bones and flint tools, covered with fluviatile loam, 20 to 40 feet thick. 3. Higher level gravel with similar fossils, and with overlying loam, in all 30 feet thick. 4.
But, as a general rule, the fluviatile species are smaller, smoother, and more globular than the marine; and they have never, like the Neritae, the inner margin of the outer lip toothed or crenulated. Potamides cinctus, Sowerby. The Potamides inhabit the mouths of rivers in warm latitudes, and are distinguishable from the marine Cerithia by their orbicular and multispiral opercula.
That there has been land as well as sea at all former geological periods, we know from the fact that fossil trees and terrestrial plants are imbedded in rocks of every age, except those which are so ancient as to be very imperfectly known to us. Occasionally lacustrine and fluviatile shells, or the bones of amphibious or land reptiles, point to the same conclusion.
A succession of low ridges seemed there to mark the extent of its basin, nor did I perceive in the country beyond any ranges of a more decidedly fluviatile character. The average breadth of the river at the surface of the water, when low, is about fifty yards, but oftener less than this, and seldom more.
These facts must be interesting to geologists, since attention has been fixed on the fresh-water formations, and the curious mixture of marine and fluviatile petrifactions sometimes observed in certain very recent rocks. The port of Barcelona has maintained a very active commerce since 1795.
Instead of the growth of coralline limestone, let us suppose, in some other place, the continuous deposition of fluviatile mud and sand, such as the Ganges and Brahmapootra have poured for thousands of years into the Bay of Bengal.
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