28 THE THAMES AND ITS TRIBUTARY RIVERS. CHAP. 



was told by one of the soberest of that calling 1 , that he once knew 

 a hatchet casually fall overboard into the river near Wallingford, 

 which was afterwards brought up and found in one of these ice- 

 meers/ 



The Rev. J. C. Clutterbuck, of Long Wittenham, in a letter 

 to the Royal Commissioners on the Thames Drainage, 1866, pre- 

 sents the results of his personal attention to the phenomenon. 



'The formation of ground-ice at the bottom of the stream is 

 another cause of obstruction. The ground-ice, when it rises under 

 the influence of the sun, lifts the stones and gravel to the surface; 

 these masses float down the stream till they lodge in certain 

 localities, and increase the natural obstructions. This ice does not 

 usually form except under a temperature of the air below 20, as 

 in January 1857 and December 1859. 



' Subsequent observation has confirmed the statement that it 

 requires a temperature of 1 2 of frost, and this usually two con- 

 secutive nights. It has been found that the whole body of the 

 water is at 32 at the time when tested. 



' The ice when seen at the bottom has the appearance of masses 

 of half-melted snow, and is formed at the tail of weeds, around 

 stones, which it lifts to the surface when it rises, about sunrise, 

 or usually soon after. When examined the mass consists of laminae 

 and spicula of ice, attached to each other at various angles, as 

 though the formation progressed as new eddies were created by 

 the forming of these laminae. I have seen pieces of rock eight 

 pounds in weight raised by a mass from the bottom, and carried 

 down the river. 



1 The formation prevails in the sharp-running shallows, and is 

 said not to take place under bridges, nor below the junction of 

 the Thame and the so-called Isis near Dorchester, where the river 

 runs over the upper green-sand in which there are springs. The 

 shifting of gravel and its deposits, especially below weirs through 

 which the ice is carried, is very great; the whole surface of the 

 river sometimes is nearly covered with the floating masses, most 

 of them carrying down sand and stones, and of course depositing 

 them where the ice lodges or is broken up at weirs, &c. 



f I am told that the ice forms at the sides of open sluices, which 

 it gradually fills up, and around the posts, &c. Every obstruction 

 causes an eddy, and in these eddies the ice forms V 



f Report of the Thames Commissioners, Appendix I. 1866. 



