A HISTORY OF BEDFORDSHIRE Thames, and attains an elevation of about 800 feet at the highest part of the Dunstable Downs between Kensworth and the Five Knolls. Al- though the most striking feature of the county, these hills do not present abrupt or rugged outlines, their contour being rounded and gently un- dulating, the result of very gradual and long-continued sub-aerial denu- dation. THE CONCEALED PALEOZOIC LAND-SURFACE Owing to the absence of deep borings in Bedfordshire we are without any actual knowledge of the disposition of the Palaeozoic rocks which underlie the Mesozoic strata, but we may form some idea of it from the facts which borings made beyond the limits of the county have revealed. A few miles to the south-east a ridge of Silurian rocks underlies Hertfordshire at a depth of about 800 feet, the strata dipping to the south at a high angle, and upon the southern flanks of this old ridge repose Devonian rocks dipping a little west of south at a much less inclination. A few miles to the west or north-west, in Northamp- tonshire, the Carboniferous Limestone has been met with at a depth of 980 feet. The Coal Measures occur at a great depth in Oxfordshire and come to the surface in Warwickshire. From this evidence, and that afforded by other borings at a greater distance, we may infer that the old Silurian ridge of Hertfordshire is the southern fold of an anticline which probably passes under Luton and is flanked on its northern fold by Devonian rocks which extend at least so far to the north as Bedford. This ancient land-surface sinks as it trends from east to west, in which direction the Devonian rocks are succeeded or overlaid by Carboniferous, but it is scarcely likely that any more recent division of that series than the Carboniferous Limestone comes on within the county. There may however be, in the north, a syncline or the southern margin of one in which the Mill- stone Grit may lie, possibly succeeded by the Coal Measures. During Permian and Triassic times this area, with the whole of the south-east of England from Norfolk to Kent and Sussex, was prob- ably a land-surface over which rivers flowed ; in the earlier period to- wards the north, depositing their sediment in the lakes or inland seas which existed just before the close of the Palasozoic epoch ; and in the later period, after a further upheaval of the land, in a westerly direction towards the more extensive sea which, at the commencement of the Mesozoic or Secondary epoch, divided the east of England from Wales and western Devon. The shore-line of this Triassic sea, which we know from its deposit of rock-salt to have been land-locked, was some distance to the north of Bedfordshire but not far from its western border. In the succeeding Liassic period, with which Jurassic times commenced, owing to the gradual sinking of the land, the sea became oceanic, en- croaching upon the area which now comprises the county and laying down sediment within it. It is at this point therefore that our certain knowledge of the geology of this district commences. 2
