xviii. ICE-DRIFT. FORCE OF CURRENTS. 463 



and slopes occupied by abundant pebbly deposits, among which 

 angular or slightly worn masses of stone, above a foot or 2 or even 

 4 feet in longest diameter, are found; solitary specimens from 

 some distant point, but within the drainage. It combines well 

 enough with the idea of expanded sheets of water in the upper 

 drainage of the Thames, about Eynsham, Oxford, and Abingdon ; 

 where such masses are not very uncommon in broad tracts of gravel 

 beds which indicate such surfaces. 



If we take the only other view, viz. that of strong currents 

 of water competent to move such stones, some facts of importance 

 appear hostile. First, such currents must have left more than 

 solitary memorials of their velocity, which in the case of a four- 

 foot block cannot be reckoned at less than 15 feet in a second, 

 such as none but an Alpine river is known to attain ; next, the 

 blocks must have been rounded, for with that velocity they could 

 only be moved step by step for short distances, by powerful inunda- 

 tions ; thirdly, the directions in which they appear to have been 

 moved are such as not to fit the idea of their being drifted on 

 the bed of flowing streams of any kind. We may add their oc- 

 currence in and upon gravel which could not have remained to 

 support them under the influence of such a current. 



VALLEY OR LOW LEVEL GRAVEL. 



Gravel is plentiful in the course of the Thames from the point 

 where the several feeders enter the great vale which extends from 

 Cricklade eastward ; but it is not at all abundant along the course, 

 and is quite scarce about the sources and in the upper branches 

 of the streams which rise in the Cotswolds, and in the region 

 between Evenlode and Cherwell. The upper parts of most of these 

 valleys have the aspect of having been ' cleared out' by decurrent 

 water. 



The broad depressed tract about Down-Ampney and north of 

 Cricklade is occupied by a nearly level deposit of gravel, composed 

 mostly of small waterworn oolitic stones with some admixture 

 of flints, to a depth of 6 or 8 feet. Near Minety there is a local 

 drift of flints, now in use on the roads, but that is to be regarded 

 as a part of the ' hill deposits ' remodelled in lower ground. The 



