Page:VCH Kent 1.djvu/43

 GEOLOGY IF our study of the geology of Kent were to be confined to the strata which constitute the surface only, we should find its rock structure so faithfully reflected in its simple physical features that a knowledge of the shape of the ground would almost necessarily convey an idea of the broader outlines of its stratigraphy. The rising ground south of the Thames, composed of the soft Tertiary clays and sands ; the bold range of the North Downs, formed by the Chalk emerging from beneath these and terminating southward in a steep escarpment ; the hollow at the foot of this range, where the underlying Gault Clay reach the surface ; the lower range of hilly ground running parallel to the Downs, composed of the harder beds of the Lower Greensand, which come next in downward stratigraphical succession ; the broad plain south of these hills, underlain by the Weald Clay ; and finally the pleasant rising ground along the southern margin of the county, where the sands and sandstones of the Hastings Series emerge from beneath the Weald Clay — all these features of the surface are directly due to the character of the strata and to the direction in which the beds are sloping. As a glance at the accompanying geological map will show, the different formations extend approximately east and west in more or less continuous belts across the county. They are prolonged beyond its borders in nearly the same direction westward through Surrey and into Hampshire, their course or ' strike ' being boldly indicated by the prevalent lie of the hill-ranges. But our investigation must not be limited to the rocks to which the surface features of the county are due ; for we have of late years learnt much regarding the strata buried deeply underground, that have no effect upon the present outline of the land. Indeed our knowledge of the deep-seated geology of Kent has recently made more important advances than that of almost any other part of the British Islands, in consequence of a series of deep borings carried down in search of coal, which have given definite information as to the downward succession of the strata to a great depth. Thus, of the three main divisions adopted for the fossiliferous rocks in the geologist's time-scale, the beds occurring at the surface in Kent represent portions only of the Cainozoic or Tertiary and of the later part of the Mesozoic or Secondary division. We now know however that the strata beneath the surface range downward to the base of the