76 J. HOPKIN'SON — THE CHADWELL SPRING 



Watford Nat. Hist. Soc.,' Yol. I, p. 137.) There must, however, 

 have been some grounds for the idea that the Bourne flowed once 

 in every seven years; it must at least have flowed about seven 

 years before 1873, probably in 1866, and that it did so is 

 corroborated by the rainfall, as mentioned by Sir John Evans in 

 this paper. He also states that it flowed in 1853, and probably in 

 1860, and this date is confirmed by Mr. Littleboy in a short note 

 on "The River Bourne" which appeared in our 'Transactions' 

 in 1883. ('Trans. Herts. Nat. Hist. Soc.,' Vol. II, p. 237.) 

 Mr. Littleboy here says: "I may mention that during thirty 

 years prior to 1860, the Bourne only overflowed its banks in the 

 garden through which it passes opposite the Bourne End mill on one 

 occasion." From this it may be inferred that not only did it flow 

 in 1860, but that it also overflowed into this garden, but no 

 further particulars of its flowing then are given. We have, 

 therefore, intervals of seven, six, and seven years between the 

 appearance of this intermittent stream before the year 1873. 

 Since then it flowed much more frequently up to the year 1883, 

 during the wettest period in our Hertfordshire record, from which 

 time fourteen years elapsed before it again flowed last year. 



I have seen the Hertfordshire Bourne at one time rising about 

 a mile up its vallev, a mile, that is, above its confluence with the 

 Bulboume ; at another time at Bottom Farm, two miles up ; at 

 another where Harratts End Lane crosses its valley, a mile further 

 up ; and at other times still higher. The position of the spring 

 from which it rises varies from time to time, sometimes being much 

 higher up the valley than it is at others, but however high the 

 Bourne may rise, there can be little doubt but that the spring at 

 its ultimate source is but one of several by which its volume is 

 successively augmented lower down the valley. 



In 1883 the Bourne commenced to flow at Bourne End; I last 

 saw it flowing on the 19th of June, 1897, from half a mile to 

 a mile higher up the valley. "When rising at these low points the 

 plane of saturation of the Chalk was evidently only slightly raised 

 above its normal height, its angle with the horizontal being a small 

 one, but when rising at the highest point, the highest on record 

 being in the third field above Harratts End Lane, this plane must 

 have been much more raised, forming a greater angle with the 

 horizontal. Then the stream would probably be augmented by 

 springs at each point lower down its valley where it has risen at 

 any other time, for if springs rose at these points when the plane 

 of saturation was less inclined, they would surely continue to rise 

 when the inclination was increased. When there is a slight rise 

 in the ground the stream sometimes disappears, appearing again 

 lower down, so that it may, perhaps, be rather looked upon as 

 a stream which flows partly underground and partly over the 

 surface, than as one which rises from a spring and is augmented by 

 springs on its course. 



The Bourne usually commences to flow between January and 

 April, frequently some time after the rain which causes it to flow 



