Page:Popular Science Monthly Volume 22.djvu/83

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point for surveying the conditions of life in Southern Britain while they were being accumulated. The visitor in Stoneham's Pit at that place sees a brick-pit several hundred yards in extent, composed of sand, shingle, and mud-banks, containing land and fresh-water shells and numerous fossil bones resting where they happen to have been dropped by the current, and these strata he can follow until they abut on the chalk forming the ancient side of the river. The land-shells have evidently been swept down by the ancient Thames from its higher reaches, and the fresh-water species have for the most part lived where they are now found, in the old river-bottom. These last are now living in our streams and lakes, with the three following exceptions. A small bivalve (Cyrena fluminalis), there very abundant, has long ago forsaken the rivers of Europe. It still, however, lives in the Nile and in the streams of Cashmere, and probably also in the rivers and freshwater lakes of Siberia, and is also used as food by the poorer people inhabiting the banks of the rivers of the great plain of China. A fresh-water mussel (the Unio littoralis) still thrives in the rivers of France, in the Seine and Loire; and a tiny fresh-water snail (Paludina marginata) abounds in the streams of Southern France. Thus in the ancient Thames at this time fresh-water mollusca now living in Britain were to be found side by side with species now to be sought in the rivers of France or of Asia. The fossil remains of the mammalia scattered through the brick-earths as they were dropped by the current have been discovered in astonishing numbers, and most of them consist of isolated fragments, such, for example, as a broken skull of the musk-sheep. Huge tusks of elephants lie side by side with antlers of stags and skulls and bones of bisons and horses. Sometimes entire limbs have been preserved with bones in place, and in one case the entire skeletons of a family of marmots surprised in the attitude of hibernation, with paws over their noses, young and old together, stand out from a block of hardened loam. Such as these are the materials for working into a picture the conditions of life in the valley of the Thames while these fluviatile deposits were being formed.

The distinct was then haunted by many extinct wild animals, and by living species no longer found together in any part of the world. Stags and roe-deer lived in the forest side by side with the gigantic and extinct Irish elk, the woolly rhinoceros, and the straight-tusked elephant. Three kinds of rhinoceros, one of them covered with wool and hair, fed on the branches and the undergrowth; wild-boars plowed up the ground in search of food, and the glades afforded pasture to innumerable horses, bisons, and large horned uri; and, when forest and glade were alike covered with a snowy mantle, a few musk-sheep, now the most arctic of all the herbivores, were to be seen on the banks of the Thames in Kent. Among; the smaller animals we may note the pouched marmot and the water-rat. These animals were kept in check by numerous beasts of prey; the smaller of them by