CUALK W.VTKK IX UK.UTS. 



improbable may be attributed to a local change in the dip of the 

 chalk, consisting of a gradual depression along the escarpment of 

 the tcrtiaries . . . from Hatfield ... to E.ye House . . . 

 at an inclination of about 20 feet per mile, the line of which is 

 nearly at right angles to the general dip of the Chalk." It is to 

 be noted, however, that such a fall in the level of the boundary- 

 line between the Chalk and the Tertiary beds, which I presume is 

 what is alluded to, does not always imply a local change in the 

 dip, but may be owing rather to the cutting back of the beds 

 somewhat down the plane of the ordinary dip. 



Then he goes on to say: "There is, however, another feature 

 lying beyond the watershed drainage area of the Lea which there 

 can be little doubt has an important bearing on the source of these 

 springs, viz., the existence of an isolated clay catchment basin of 

 23 square miles, which has no direct surface outfall, the central 

 and lowest part of which is between North and South Mims where 

 the surface is chalk, and several swallow-holes exist in the locality 

 which receive and absorb the drainage water of the district. The 

 natural tendency in this case would be for the waters to flow in 

 the direction of the general dip of the chalk basin, but from the 

 inclination of the strata towards the east, there can be no doubt 

 a considerable portion of the water is carried off in that direction. 

 There is a small ridge at North Mims separating this catchment 

 basin from the Colne valley, the entire volume of the drainage 

 shoots down fi'om off the clay lands on to the chalk, and pours 

 into numerous swallow-holes and entirely disappears." 



The above remarks refer only to a probable oiigin of springs 

 between Ware and Hoddesdon, but further on the following 

 words occur: "The source of the Chad well spring, though deep 

 seated, may possibly be influenced from the same circumstances." 



Let it be understood that whilst questioning the explanation of 

 the clouding of the spring-waters from the suspended matter taken 

 into the Chalk by water at the surface 9 or 10 miles off, I do not 

 dispute the northerly underground flow of much of the water that 

 sinks into the Mimms swallow-holes. That it goes so far eastward 

 as Chad well and Amwell is, I think, open to doubt. 



Swallow-holes. 



These remarks naturally lead to the subject of swallow-holes, 

 and it is perhaps well to explain here that these are hollows into 

 which small streams disappear. 



They are usually found close to the junction of the Tertiary beds 

 and the Chalk, the water flowing down the clay-slopes and sinking 



