the Upper and Lower Drift of the Eastern Counties. 401 



place as lying upon the deeply eroded face of the Eocene tertia- 

 ries j but, being unfossiliferous, he does not identify them. A 

 reference, however, on M. Dumont's map to the place where 

 this section occurs leaves no doubt that the covering sands 

 shown in the section are those mapped by M. Duraont as the 

 sables campiniens. A short distance south of this place the 

 sands pass beneath the Loess that, according to M. Dumont, 

 caps the heights on either side of the valley at Brussels. 



The precise margin of the lower-Drift bay, which, as I have 

 shown, can be detected accurately at one part of Essex, appears 

 to be obscured in Belgium beneath the Loess. By analogy and 

 by assuming a uniformity of depression over either area to have 

 taken place on the introduction of the upper Drift, we may infer 

 that the margin of this bay in Belgium passed along the northern 

 flank of the Ardennes, from which it derived the quartzites that 

 constitute so considerable a proportion of its included pebbles, 

 the Loess spreading over this margin and concealing it, as is the 

 case with the western margin, that, in Essex, passes under and is 

 hidden by the Boulder-clay. 



In another section, given by Sir Charles Lyell, he shows the 

 Loess at Tournay to rest upon the lower beds of the Eocene series, 

 which there crop out, at their original margin of deposit, without 

 (so far as the section represents) any intervening bed of sand or 

 rolled stones. It would thus appear that the margin of the 

 lower- Drift bay passed to the north of Tournay. In another 

 section at Dileghem,two miles N.N.W. of Brussels, Sir Charles 

 shows the Loess resting upon a bed of sand, which, although un- 

 fossiliferous, he refers, from similarity of appearance, to the same 

 sands as those described by him at Cassel as belonging to the 

 Diest group. The Diest sands, however, are not indicated by 

 M. Dumont anywhere west or south of a point about ten miles 

 north-east of Brussels — a still greater distance from Cassel. 

 Dileghem, where this section occurs, is represented by M. Du- 

 mont as at the margin of the Loess and the Campinian sands, 

 where the latter pass under the former. It would seem, there- 

 fore, that the unfossiliferous sands of Dileghem, upon which the 

 Loess rests, belong to the Campinian series, the more especially 

 so as we have seen that at Dieghem, a few miles only N.E. of the 

 former place, the Campinian sands shown to occur there by M. 

 Dumont agree with Sir Charles's section of that place. If, there- 

 fore, the Loess at Dileghem is underlain by the Campinian sands, 

 the margin of the lower-Drift bay would pass somewhere be- 

 tween that place and Tournay ; but if otherwise, it would pass 

 between Dieghem and Dileghem. I, however, for the reasons 

 stated, strongly incline to the former alternative, and I have 

 adopted it in the hypothetical extension of the boundary given 



