232 
THE GEOLOGIST. 
A portion of the skull of Mastodon latidens, from Perim Island, in the 
Gulf of Cambay, vras exhibited by C. S. Mann, Esq. 
CiYiL Engineers.— 3. — " On the Perennial and Flood Waters 
of the Upper Thames," by the Eev. 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 containina^ a coniputated area of 1500 square miles, situated be- 
tween the range of chalk hills bounding the vales of Aylesbury and of 
White Horse, and the Cots wold 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 Kvenlode, 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 condition 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, 
M-hich rested on a ridge of the clay. As a rule, the lower levels of the 
valley, including also in many places the oolitic rock, outci'opping to the 
north at a very slight angle beneath the Oxford clay, ^ ere 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 j^hysical 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 they 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 
stream was beset w ith 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 this communication to deal with absolute quantities de- 
rived from the various sources, yet it was believed the following gaugings, 
