xvn. LONDON BASIN. 451 



within the old sea-basin of the Thames. The most distinct hy- 

 pothesis of such an origin of the clays and sands and ferruginous 

 elements of the London eocenes is that investigated by Lyell, 

 Prestwich, and others ; which ascribes to the anticlinal elevation 

 of he Wealden the origin of currents flowing to the northward 

 and carrying the spoils gathered in their courses. We must not, 

 for this transport of material, confine our view to the actual valleys 

 which contain rivers now running ; though it is probable that these 

 hollows were really sketched out during the elevation of the 

 Wealden ; it is enough to observe that the height of the interior 

 ridges of Kent and Sussex, from which the sands, clays, and iron 

 oxides might come, was probably far greater at the time of their 

 utmost elevation than now; while, in fact, the obvious and 

 enormous waste from these ridges may well be appealed to in 

 support of the hypothesis. 



If it be objected that separate fossils, and fragments of the 

 peculiar sandstones, shell limestones, and argillaceous carbonates 

 of iron which abound in the Weald should be often met with 

 in the London strata, the answer may be, that if the transport 

 were by ordinary rain and river action along gentle slopes in a 

 mild climate, only fine-grained sediments, such as now descend 

 the Thames and its branches, ought to be looked for. 



To some extent these arguments apply also to the country north 

 of the Thames drainage, and indeed to the whole range of the 

 oolites in the upper valleys of the Thames. All this country has 

 been wasted; there is no reason to deny that it was elevated so 

 as to be capable of waste during the eocene periods ; and the 

 inclination of the strata is uniformly indicative of a general rise 

 parallel to an axis from south-west to north-east. 



Within the narrow sea, thus supplied with sediments, the dis- 

 tribution of these is found to be such as to determine in some 

 degree the direction of currents, depth of water, and other con- 

 ditions by which the successive deposits were affected. The lowest 

 or Thanet beds of sand seem to be unknown in the western parts 

 of the old bay, and to grow thicker from the middle eastward. 

 The Woolwich beds of laminated clays, sands, and pebbles products 

 of shallow water, varying streams, and perhaps oscillations of 

 level have more uniform distribution in the area, though the 

 mottled character of the deposit is most observed in the west, 



Gg 2 



