Vol. 68.] STAGE IN THE YALLET OF THE EIVEK LEA. 225 



On considering all these data, it appears to me that one is 

 justified in provisionally placing the Ponder's End Stage opposite 

 the line marked in the table (p. 223) as 8. xx, a period about which 

 we at present know so little. 



In the view of those who may not accept the minuter sub- 

 divisions of the Palaeolithic Epoch, I think that the general 

 succession of the correlations given in the table will still hold 

 good, although the details will be more indefinite. 



YI. The Eelation of PALiBOLiTHic Man to the 

 Glacial Period. 



The evidence of the Ponder's End deposit supports in a remarkable 

 manner the contention of those who have maintained that Palaeo- 

 lithic man in this country is interglacial. Eor although it is, of 

 course, undeniable that Paleolithic man is later than the maximum 

 glaciatiou of this country, there can yet be no doubt that after 

 Palaeolithic man had left these shores, even the southern part of 

 this country passed through a spell of Arctic cold. 



To my mind, the evidence of the Ponder's End Stage puts into 

 our hands the key to many outstanding difficulties, particularly with 

 regard to the conflicting nature of the evidence upon the relation- 

 ship of early man to the Glacial Period. That Palaeolithic man is 

 later than the Chalky Boulder Clay has been proved over and over 

 again, beyond any possibility of doubt. Put at the same time there 

 are frequently contorted drifts overlying the Palaeolithic deposits 

 which are at least strongly suggestive of Glacial action. These have 

 been described by Sir Joseph Prestwich, jMr. Worthington Smith, 

 Prof. Sollas, and many others. They are, indeed, familiar to every 

 collector of flint-implements. I believe, with Mr. Worthington 

 Smith, that these post-Pa] fceolithic contorted drifts should be 

 grouped with the ' Trail ' of the Eev. Osmond Eisher. And there- 

 fore, if the officers of the Geological Survey be right in identifying 

 the Trail with the Low-Level River Drift, these contorted drifts also 

 become linked to the Ponder's End Stage. 



One of the most striking exposures of the Trail that I have seen 

 was in a brickyard at Hoddesdon, which was open in or about the 

 year 1896, but has now been closed for some time. There the Trail 

 had ploughed its way through a Palaeolithic river-drift gravel about 

 4 or 5 feet thick, and had folded this gravel back upon itself through 

 an angle of 180°. Part of its material was composed of re- 

 distributed Boulder Clay, and was practically indistinguishable from 

 that deposit. 



The Lea Valley is cut through the plain of Chalky Boulder Clay, 

 and is therefore later than that formation. The Palaeolithic river- 

 drifts of this valley, of which the Hoddesdon deposit is one, can be 

 further shown to be post-Chalky Boulder Clay by the erratic rocks 

 that they contain, the Glacial deposits being the only source of 

 local derivation for these erratics. Yet the Palaeolithic gravels 



