in. GROUND ICE OF THE THAMES. 27 



now traversed by trie Great Western Railway, which passes very 

 near to Thames Head. 



The supply of water once delivered from the ' true head of 

 Thames ' is not easily to be inferred from the now contracted dis- 

 charge at a point lower down the valley; this being- what remains 

 after the leaky summit level of the Thames and Severn Canal has 

 been satisfied. Mr. Taunton states the supply at from 350 to 400 

 cubic feet in a minute, and never knew it to be less than 300 feet. 

 The water is collected in the joints and cavities of the upper Bath 

 oolite, above the argillaceous bed of FullerVearth, which is here 

 27 feet thick. 



Lower down are the Ewen springs, which yield 150 feet per 

 minute on an average, so that fully 500 cubic feet in a minute are 

 commonly yielded by these springs' 1 about the very head of 

 Thames. 



The water of the Thames is said to have at least two uncommon 

 properties : one is to be subject, when placed in casks and carried 

 to sea, to a clarifying fermentation which yields inflammable gas, 

 and leaves the liquid purer and more appropriate for use than any 

 other water e ; the other is to freeze at the bottom, when the 

 stream is flowing freely above. Some other examples have been 

 cited of this peculiarity, but this of our own river seems to be the 

 most remarkable and best-attested by repeated observation. Dr. 

 Plot, in his Natural History of Oxfordshire, gives the following 

 account : e I find it the joint agreement of all the watermen here- 

 about that I have yet talked with, that the congelation of our river 

 is always begun at the bottom, which, however surprising it may 

 seem to the reader, is neither unintelligible nor yet ridiculous. 

 They all consent that they frequently meet the ice-meers (for so 

 they call the cakes of ice thus coming from the bottom) in their 

 very rise, and sometimes in the underside including stones and 

 gravel/ and adds, 4 as to the matter of fact, as I cannot but think 

 it hard that so many people should agree in a falsity, so methinks 

 'tis as difficult they should mistake in their judgments, since I 



d Minutes of Proceedings of Institute of Civil Engineers, 1862-1863. 



e ' The Thames water at sea, in eight months' time, acquires so spirituous and 

 active a quality, that upon opening some of the casks, and holding the candle near 

 the bunghole, its steams have taken fire like spirit of wine, and sometimes en- 

 dangered firing the ship.' Plot, Hist. Oxf., p. 26. 



