OF THE XEIGH130IJEH00D OF WATFOED. 127 



There is a considerable amount of water in the gravel or sand in 

 the district known as Bushey Heath, or Stanmore Common ; hence 

 of late years the population there has increased, and seems to have 

 outrun the natural water supply. The site of the village of Abbot's 

 Langley, with its hamlet Eedmont, presents a different feature. 

 The Chalk here rises to a considerable elevation — about 450 feet 

 above the level of the sea. It is capped by an outlying bed of the 

 "plastic clay," in situ, which may be seen cropping out on the road- 

 side bank between Trolly Bottom and the village. This is covered by 

 a bed of gravel in which the water accumulates. If, in sinking a 

 well, of which there are many, as well as open ponds, the clay is 

 pierced till reaching the chalk beneath, the Water will disappear. 

 At Bedmont, on one occasion at least, in order to clean out a large 

 pond fed by the natural supply from the gravel, the head or stank 

 of the pond being cut for that purpose, the water which imme- 

 diately found its way into the Chalk sensibly augmented the 

 supply of water in the wells near at hand, though at least 170 feet 

 below. 



To return to the district east and south-east of the Colne. 

 Where the London Clay is not covered by beds of sand or gravel, 

 the water is thrown from the surface sometimes augmented in its 

 passage to the river by artificial agricultural drainage ; these 

 waters flow in open water courses, which here and there furrow the 

 escarpment which overhangs the Colne. When it arrives at the 

 junction of the clay with the sand outcropping beneath it, the 

 water wholly or in part sinks into the earth through natural 

 apertures usually called swallow-holes, descends into the subjacent 

 chalk, and is added to the water in that so-called water-beaiing 

 stratum by which the river is augmented and maintained. As the 

 water which finds its way into the chalk by these swallow-holes is 

 derived from the surface drainage of the Tertiary clays, and as 

 their surface miist not only be saturated but flooded before the 

 water will be discharged from the surt'ace, the supply from this 

 source must necessarily be irregular and periodical. In some years 

 there are no such floods ; in others, such as 1875-6, the quantity 

 of water must in many cases be more than the swallow-holes can 

 take in. Among the most remarkable are those found in the 

 carrier which conveys the water from the Elstree reservou' to the 

 river, which must be plugged when the water is discharged, to 

 prevent the waste of a greater part if not the entire volume. At 

 another, near Letchmore Heath, in the parish of Aldenham, where 

 a large body of water sinks in a deep depression or pit into the 

 earth, at the junction of the sand of the Tertiary beds and the 

 Chalk, this sand may be seen cropping out close at hand. It has 

 been supposed that there is some connexion between this irruption 

 of water and the well-known copious issue of water at Otters- 

 pool. There are stories of ducks having found their way thither 

 by some subterranean passage ; and measurements of the level at 

 which the water stands in the wells thereabout and in the direction 

 of the pool, show an irregularity not easily accounted for but by 



