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THE GEOLOGIST. 



A portion of the skull of Mastodon latidens, from Perini Island, in the 

 Gulf of Cambay, was exhibited by C. S. Mann, Esq. 



Civil Engineees. — March 3. — " On the Perennial and Flood Waters 

 of the Upper Thames," by the Kev. J. C. Clutterbuck, M.A. 



The object of this communication was to draw attention to the nature 

 of that portion of the watershed of the Thames comprising; the oolitic dis- 

 trict, and containing; a computated area of 1500 square miles, situated be- 

 tween the range of chalk hills bounding the vales of Aylesbury and of 

 White Horse, and the Cotswold Hills bounding the Vale of Evesham and 

 the Valley of the Severn. It was shown that the Thames ran almost 

 entirely over a clay-bed from its source, about four miles west of Ciren- 

 cester, to its junction with the Thame stream, the limit of the district 

 under consideration ; and that it was the mere carrier of waters, whether 

 perennial or flood, brought in by its tributaries, a description of which, in 

 the order they joined the main river, was given. Those running from 

 north to south and from north-west to south-east, — as the Churn, the 

 Coin, the Leach, the Wirdrush, the Evenlode, and the Cherwell, — re- 

 ceived their perennial waters from oolitic strata. Those flowing from 

 south to north originated in the the chalk hills, from the escarpment of 

 which they conveyed the back drainage, slightly augmented by that of 

 the Upper Greensand, and then passed over the Gault and Kimmeridge 

 clays, either to the main stream, as the Eay and the Cole, or as affluents 

 of the Ock and the Thame, from which the principal supply was derived. 



The geological conditio]] of the source of the main stream was next no- 

 ticed, and it was stated that the whole natural bed of the river, from 

 Somerford Keynes to Sandford, below Oxford, was an excavation in the 

 Oxford clay, flanked to the south by the escarpment of the coraline oolite, 

 which rested on a ridge of the clay. As a rule, the lower levels of the 

 valley, including also in many places the oolitic rock, outcropping to the 

 north at a very slight angle beneath the Oxford clay, were covered with 

 drift gravel. Wherever the floods had extended, sand, silt, or argilla- 

 ceous loam had been deposited on this gravel; and this action was still 

 going on, governed by the number and character of the floods. Thus, 

 the bed of the river was, as a rule, gravel, and the banks a warp, the accu- 

 mulation of ages. There were instances of the change of bed to the ex- 

 tent of several chains in width ; and indeed there appeared to be no limit 

 to these deviations, but the physical features of the valley. These facts 

 had an important bearing on any improvement, so much needed, in the 

 drainage or condition of the Thames valley. 



The perennial waters were either used for mills or for navigation. The 

 mills on the tributaries were numerous. Between Thames Head and 

 Cricklade they were, however, virtually deprived of water. From Crick- 

 lade to Lechlade the water was not applied to any economical use ; and 

 again, from Lechlade to Wolvercote, three miles above Oxford, there were 

 no mills. The gaugings of the numerous tributaries, where tkey joined 

 the main stream, would give the aggregate of the water that it carried ; but 

 such observations had been neglected, and as the watersheds were very 

 varied, any estimate of the volume of these streams at different seasons 

 would be difficult. Most of these tributaries were immediately affected 

 by heavy rains, and were subject to flood. The gauging of the main 

 si ream was beset with other difficulties, as the height and passage of the 

 water was divided between the mills and the navigation, controlled, in- 

 deed, by stringent regulations, but too often disregarded. Though it was 

 not the purpose of tins communication to deal with absolute quantities de- 

 rived from the various sources, yet it was believed the following gaugings, 



