PROCEEDINGS OF (JEOLOGTCAL SOC'TUTTES. 



tlic result of several years' observations, by Mr. Stacy, the manager of 

 the mills at Wolvercote, would be received with interest, and would, 

 if carried out in other places, lead to valuable results. There were no 

 mills for thirty miles above Wolvercote, and the navigation, though 

 "flashes " were still sent down, had virtually ceased. Mr. Stacy had (bund 

 that, in the summer months, the river had a mean velocity of 58 feet per 

 minute, when the total yield was 8120 cubic feet per minute, exclusive 

 of the quantity brought down by " flashes," which it was difficult to 

 estimate. During the winter months, in fine weather, without frost or 

 rain, the river had a mean velocity of 94 - 9 feet per minute, and taking 

 the sectional aiva as 181'5 square feet, this gave a volume of 17,221 cubic 

 feet per minute. In moderate rainy weather, without floods, when the 

 level of the river just reached the high-water navigation mark, the total 

 quantity of water passing through the mill was 28,189 cubic feet per 

 minute. At the end of December, 1862, under similar conditions, the 

 total yield was 35,498 cubic feet per minute, of which 7738 cubic feet 

 might be taken as the water passing from the main stream to Wytham. 

 These data suggested the necessity of adopting a standard at various sta- 

 tions, so that the results might be compared with the rainfall when the 

 gaugings were taken. At the same time, observations were made on the 

 river below the influx of the Cherwell and the Ock, when the yield was 

 found to be 50,995 cubic feet per minute, being an excess of 15,497 

 cubic feet as compared with Wolvercote, and of which excess it was esti- 

 mated that 7089 cubic feet were brought in by the Cherwell, and the re- 

 mainder by the Ock and the smaller perennial streams. The verification 

 of these quantities was prevented by a fall of rain of nearly half an inch, 

 in a few hours, which, at the expiration of thirty- six hours, doubled the 

 volume of the Thame stream, and added about thirty per cent, to the 

 volume of the main river. At Wolvercote, on the 5th of January, 1863, 

 after about one inch of rain, the increase was from 27,986 to \S, 118 cubic 

 feet perminute. The rainfall from the 1st to the 7th January, 1863, inclu- 

 Bive, produced a flood in the Thames under circumstances peculiarly 

 favourable for observation. The rain recorded during this period averaged 

 1*61 inch over the whole watershed; Dalton's gauge, at llemel Ilcmp- 

 Btead, showing a fall of 152 inch, and a percolation of 1T0 inch. The 

 gaugings of the main river at Wolvercote then amounted to 82,500 cubic 

 feel pei- minute, and at Clifton Hampden, below Abingdon, to 181,832 

 cubic led per minute. Of this latter quantity 41,755 cubic feet were deli- 

 vered l>\ the Cherwell (or an increase of 37,066 cubic feet as due to the 

 flood), 24,864 cubic feet by the Ock, and 29,713 cubic feet by the many 

 smaller streams, watercourses, and land-drainage out fa lis, issuing into 

 the river between Wolvercote and Clifton Hampden, a distance of about 

 twenty miles by the river, with an average fall of two feel per mile, from 

 a computed watershed of eighty square miles. It should he stated that 

 the rainfall on this occasion, on the southern part of the district, was in 

 excess of the average more than half an inch. 



The state of the navigation bet ween Lechlade and Oxford was then de- 

 scribed. 1 1 w as remarked that from running on one stratum, the Oxford 

 clay, and from other causes, it had ceased to be; although the physical 

 condition of the river bed, and its easy gradients, oilereil facilities for na- 

 vigation ; for the whole fall in this distance, 31 miles, was only 51 feet 3 

 inches, or about 1 foot 7.' inches on an average per mile. 



The highest recorded on the Thames, since January 8, 173 I. were 



then alluded to, and details were given of thai which occurred March 



29-31,1862. The action of land-drainage on flood- water was aext con- 



VOL. VI. 2 it 



