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We travelled eight miles W.S.W. over a succession of plains separated by belts of forest, consisting of bloodwood, box, apple-gum, and rusty-gum. Some plains were scattered over with Bauhinias. The holes along the plains are probably filled with water during the rainy season; dead shells of Paludina were extremely numerous, and we found even the shield of a turtle in one of them.
BENSON, in the first vol. of Gleanings of Science, published at Calcutta in 1829, describes a species of Paludina found in pools, which are periodically dried up in the hot season but reappear with the rains, p. 363. And in the Journal of the Asiatic Society of Bengal for Sept. 1832, Lieut.
To some it may appear enigmatical how such fragile objects could have escaped annihilation in a river-bed, when flint tools and much gravel were shoved along the bottom; but I have seen the dredging instrument employed in the Thames, above and below London Bridge, to deepen the river, and worked by steam power, scoop up gravel and sand from the bottom, and then pour the contents pell-mell into the boat, and still many specimens of Limnaea, Planorbis, Paludina, Cyclas, and other shells might be taken out uninjured from the gravel.
Traced in one direction, or eastward towards Herne Bay, the Woolwich beds assume more and more of a marine character; while in an opposite, or south-western direction, they become, as near Chelsea and other places, more fresh-water, and contain Unio, Paludina, and layers of lignite, so that the land drained by the ancient river seems clearly to have been to the south-west of the present site of the metropolis.
In the same beds I found many freshwater shells of the genera Paludina, Limnaea, etc., all of living species. The plants named by Professor Heer are also Recent and agree singularly with those of the Cromer buried forest, before described.
The slug, called Succinea, is not strictly aquatic, but lives in damp places, and may be seen in full activity far from rivers, in meadows where the grass is wet with rain or dew; but shells of the genera Limnaea, Planorbis, Paludina, Cyclas, and others, requiring to be constantly in the water, are extremely exceptional in the loess, occurring only at the bottom of the deposit where it begins to alternate with ancient river-gravel on which it usually reposes.
Limnaea, similar to those of Europe, creep along the surface of the water; small Planorbis live on the water-plants, to which also adhere Ancylus; and Paludina, Cyclas, and Unio, furrow its muddy bottom. The latitude of this spot was 21 degrees 23 minutes S.
For example, in one restricted locality in Germany the shells of snails belonging to the genus Paludina have been found in superimposed strata in the order of their geological sequence.
The last irruption of salt water happened in 1824, when the North Sea entered, killing all the fresh-water shells, fish, and plants; and from that time to the present, the sea-weed Fucus vesiculosus, together with oysters and other marine mollusca, have succeeded the Cyclas, Lymnaea, Paludina, and Charae.
The upper division of this group consists in great part of beds of compact, fragile limestone, with some intercalated green marls. The shells in some parts are a mixture of Cerithium, Cyclostoma, and Corbula; in others Limnea, Cerithium, Paludina, etc. In the latter, the bones of reptiles and mammalia, Palaeotherium and Lophiodon, have been found.
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