From Luton to Hatfield the course of the Lea pursues a generally south-easterly direction; at Hatfield it becomes for a short distance due east, and then trends to the north-east through Hertford to Ware. Here it takes a sudden bend, so that the remainder of its course through the county and the adjacent portion of Essex is almost due south. A direct line from Luton to the Lea near Waltham Abbey measures about 40 miles; but, owing to its great north-easterly bend, the course of the Lea between these two points is something like 45 miles. [Illustration: Bishop’s Stortford (showing the Plain Country)] The last two rivers on our list are the Ash and the Stort, both of which in the upper part of their courses run from north to south nearly parallel with the Beane and the Quin. The Ash rises near Brent Pelham and thence flowing by Much Hadham and through the parish of Widford, falls into the Lea above Stanstead Abbots. The Stort, which is the most easterly tributary of the Lea in the county, is of Essex origin, taking its rise at the very border of the county, near Meesdon, and entering it again close to Bishop’s Stortford. Some distance above Stortford it receives one tributary from the Essex and a second from the Hertfordshire side, the latter forming for a short distance the boundary between the two counties. At Stortford the Stort is wholly within Hertfordshire, but a little below the town it forms the county boundary for a considerable distance, passing by way of Sawbridgeworth on the Hertfordshire, and Harlow on the Essex side, to join the Lea a short distance below the Rye House. From this point and Hoddesdon nearly to Waltham Abbey the Lea forms the boundary between Hertfordshire and Essex, finally leaving the former county near Waltham. The river now constitutes the line of division between Middlesex and Essex, finally joining the Thames below Bow Bridge, at Barking, after a course of 45 miles. Here may conveniently be mentioned the celebrated Chadwell spring, near Hertford, which after supplying London with a large amount of water by way of the New River (of which more in a later chapter) for three hundred years, failed temporarily in 1897, so that water began to flow into, instead of out of its basin. Previous to this failure the amount of water discharged daily by the Chadwell spring was estimated at not less than 2,600,000 gallons. In addition to the temporary failure of Chadwell, a spring in Woolmers Park, near Hertford, has of late years completely dried up; both these failures being attributed mainly, if not entirely, to the tapping of the Hertfordshire water-supply by the deep borings in London. 6. Geology and Soil. By Geology we mean the study of the rocks, and we must at the outset explain that the term _rock_ is used by the geologist without any reference to the hardness or compactness of the material to which the name is applied; thus he speaks of loose sand as a rock equally with a hard substance like granite.