243 



I which is absorbed by the very porous beds of the Under OoUte 

 i is very large, amounting to a third of the rainfall. 



The Churn, Coin, Windmsh, and Evenlode, descend through 

 valleys of denudation, the Under Oolite having been cut through 

 to some depth below their junction. A large quantity of the 

 Under Oolite rainfall finds its way into those rivers by springs 

 on the sides of those streams, and particularly by springs on the 

 North-western side of the narrow valleys through which they 

 pass; but some of this is liable to be absorbed again in its 

 passage over the Under Oolite, which occupies the beds of those 

 rivers below the junction. 



The loss by percolation through the Upper Oolite, including 

 the Forest Marble and Cornbrash, is to a considerable extent 

 compensated by the immense discharge from the Fullers Earth 

 by Boxwell, Ampney, and Bibury springs; which water, if not 

 so discharged, would pass down the plane of stratification, and 

 would not appear again in the vale of the Thames ; and added 

 to which must be reckoned half of the water pumped up from 

 the Fullers Earth by the engine at Thames Head. The summit 



■ level of the Thames and Severn Canal extends from Daneway, 

 ' at the Western end of Sapperton tunnel, to Siddington, near 

 / Cirencester, being about eight miles in length. From those 



two extremities the canal descends, westward towards the vale 

 of the Severn, and eastward to the vale of the Thames. The 

 water being retained on the summit by means of locks, it 

 descends in either direction — about half to the Thames, and 

 the remainder towards the Severn. The principal loss in the 

 Watershed of the Thames occurs in the Under Oohte, the area 

 /• of which is about 106 square miles. I have many years been 



■ aware of the great loss of water in the Churn, Coin, Windrush, 

 and Evenlode, by passing over the open and rubbly rock of the 

 Under Oolite, but until 1859 did not succeed in getting the 

 occupiers of the mills on those streams to fix on the right cause ; 

 and this was not accomplished without a thorough investigation 

 of the Chum, in which I lent a helping hand, and which finally 

 established the views I had for years previously entertained. 

 The observations were made in the autumn of a very dry 



