From the great central boss of the chalk system in Salisbury Plain, two long cretaceous horns or projections run out to eastward towards the Channel and the German Sea. These two horns, separated by the deep valley of the Weald, are known as the North and South Downs respectively. The first great spur or ridge passes through the heart of Surrey, and then forms the backbone of Kent, expanding into a fan at its eastward extremity, where it topples over abruptly into the sea in the sheer bluffs which sweep round in a huge arc from the North Foreland in the Isle of Thanet, to Shakespeare's Cliff at Dover. The second or southernmost range, that of the South Downs, parts company from the main boss in Hampshire, and runs eastward in a narrower but bolder line, till the Channel cuts short its progress in the water-worn precipice of Beachy Head. Between these two ranges of Downs lies the low forest region of the Weald, and between the South Downs and the sea stretches a long but very narrow strip of lowland, beginning at Chichester, and ending where the chalk cliffs first meet the shore beside the new Aquarium and Chain Pier at Brighton. Thus the whole of Sussex consists of three well-marked parallel belts: the low coast-line on the south-west, the high chalk Downs in the centre, and the Weald district on the north and north-west. As these three belts determine the whole history and very existence of Sussex as an English shire, I shall make no apology for treating their origin here in some rapid detail.