For in those days Europe, though even then little more than a great peninsula, extended far beyond its present limits. England and Ireland were still part of the mainland, and great rivers flowed through the broad valleys that are now the Irish Sea, the North Sea, and the English Channel--rivers that counted the Seine, the Thames, the Garonne, and even the Rhine, as mere tributaries. The Strait of Gibraltar was then the Isthmus of Gibraltar--a narrow land bridge connecting Europe with Africa. The Mediterranean was then an inland lake, or rather two inland lakes, for Italy and Sicily stretched out in a broad, irregular mass to join the northern coast of Africa, while Corsica and Sardinia formed a long peninsula extending from the Italian mainland and almost, if not quite, reaching to the African coast. THE THAMES VALLEY IN CHELLEAN TIMES The interpretation of the features of stratification in the valley of the Somme is especially interesting because it gives us a key to the understanding of a similar sequence of prehistoric events in the valley of the Thames. The station of Gray's Thurrock in this valley is barely 120 miles distant from the Chellean station of Abbeville, in the valley of the Somme, and it is apparent that the old flint workers were freely passing across the broad intervening country and interchanging their ideas and inventions. Thus it happened that Chellean implements identical with, or closely related to, the types of the Somme valley were being fashioned all over southern Britain from the Thames to the Ouse. The ancient River Thames (Lyell,(28) Geikie(29)) was then flowing over a bed of boulder-clays which had been deposited during the preceding glaciations. Its broad, swift stream was bringing down great deposits of ochreous gravels and of sands interstratified with loams and clays. It is these old true river-gravels which display their greatest thickness on the lowest levels of the Thames and which are largely made up of well-bedded and distinctly water-worn materials. On these low levels the flint workers sought their materials, and here they left behind them the archaic Chellean implements which are now found embedded in these older river-gravels, just as they occur in the gravels washed down over the three terraces of the Somme and the Marne. In the Thames this old gravel wash seems to have been down-stream, whereas on the middle and upper terraces of the Somme the gravel wash came directly down the sides of the valley, except, perhaps, in very high floods. These deep beds of gravel, sand, and loam lie for the most part above the present overflow plain of the Thames, although in some places they descend below it; which proves that the main landscape of the Thames also, except for the changes of the flora and of animal life, was the same in Pre-Chellean and Chellean times as it is at present. Thus the Somme, the Thames, and the Seine had all worn their channels to the present or