Page:VCH Hertfordshire 1.djvu/63

 GEOLOGY here the earliest traces of man ; but since the lake-bed was visited by Mr. Clement Reid a few species of mammals have been added to his list and a few flint implements have been found associated with them in this silt. It therefore seems probable that primaeval man lived on the shores of this lake and there fashioned his rude implements of flint, but we cannot be certain that this was the period of his arrival in Britain. We do not find the remains of man in these deposits, but only the results of his handiwork in rudely-chipped flints. If, therefore, man existed in Britain before he became a tool-maker we should have no trace of such existence. In a somewhat similar situation near Caddington Mr. Worthington Smith has found a workshop of Palaeolithic flint implements ; he has found the cores from which chips have been struck, and he has found the chips struck ofF them and pieced them together again. Here there are also other indications of human habitation, and, as at Hitchin, by the side of a lake. With the advent of man the geological record ceases and the archaeological begins, but there are other superficial deposits which have not yet been noticed. Such are the detritus of existing rivers, whether gravel or alluvium, sometimes much higher than their present level, showing how deep they have cut down their beds ; and accumulations of peat resulting from vegetable growth on boggy land. There are also deposits to which no definite age can be assigned, in addition to those of which the age is a subject of controversy. The formation of ' pipes ' in the Chalk has been going on ever since the Chalk was raised above sea-level and water percolated into it ; and ever since the Tertiary beds were removed from the surface of the Chalk, that surface where exposed has been ' weathered ' into clay-with-flints, this bed, which covers much of the Chalk in western Hertfordshire, being the result of surface-disintegration of chalk. Much of our brick-earth has also been forming for an indefinite period. A brief summary may now be given of the foregoing attempt to trace the history of Hertfordshire before the advent of man, from which period the story will be continued by Sir John Evans. The scene opens with a deep sea in which a calcareous deposit was forming a sea teeming with the abundant life which characterized the Upper Silurian period. The nearest land-surface was a plateau of Cambrian rocks in the centre of England, the sea extending on the south to western France, where it washed a shore of Cambrian and Lower Silurian rocks. The sea-bed rose, and the calcareous mud, consolidated into shale and limestone, became crumpled up into folds running east and west, and on the southern flank of one of these folds there was sea in Upper Devonian times, also replete with life. This sea-bed rising, its sediment, consolidated into shale, remained for long ages a ridge of land stretching across Middlesex and the south of Hertfordshire, the highest part of this land being the Silurian hills on the north. Further crumpling or folding in nearly the same direction as before affected this Devono-Silurian tract so that the portion of it which has been dis- 25