GEOLOGY. 



At the point where Rhine and Maas leave the hilkcountry and enter the plain 

 their ancient high4evel terraces combine, spread out into a wide somewhat undulating 

 plateau, and occupy the whole area now separating the two rivers. This high plateau 

 is the head of an ancient delta, most of which has been destroyed by the action of river 

 or sea; so that the edges of the plateau now form steep scarps, either facing the Rhine 

 or overlooking the plain of the Netherlands. 



The deposits of this delta consist mainly of current*bedded sand and sandy 

 gravel, partly derived from the basin of the Rhine, partly brought down by the Maas. 

 They contain, however, subordinate beds of freshwater clay and lignite, on at least two 

 different horizons. These masses of clay, which vary from 1 to about 5 metres in thick* 

 ness, were laid down in abandoned river*channels, or shallow lakes, and were probably 

 never continuous over long distances. After their deposition, as the level of the delta 

 rose, they were covered by sheets of sand and gravel, like those below; and in this 

 process there was a certain amount of breaking up and destruction of the claysbeds, 

 for large pebbles of fossiliferous clay are often found in the gravel — indeed in some 

 cases clay*pebbles with plant*remains are the sole relic of a once*continuous clay*bed. 



The total thickness of the delta*deposits is still unknown. It is probably at least 

 100 metres; but the complete sequence has not been proved at any one spot. Tectonic 

 disturbances have affected the delta, and were probably in progress whilst the delta 

 was being formed; it is therefore impossible to estimate the thickness of the delta* 

 deposits by measuring from the maximum height of the gravel plateau to the maximum 

 depth to which the gravels descend beneath the level of the sea. 



We must not make the mistake of estimating the importance of the ancient delta 

 by the small remains now preserved between the Dutch lowlands and the Rhine. At 

 the period of its maximum extension the fan stretched right across the North Sea, 

 and gravels evidently derived from the Rhine and Maas are found abundantly in the 

 so*called "Cromer Forest*bed" of the Norfolk coast. We do not yet know whether any 

 part of the high*plateau between the Rhine and Maas belongs to this maximum extension ; 

 but the Cromerian fauna and flora should be searched for on the highest parts of the 

 plateau. Only rivers flowing at that high level could form a gravelly delta as far away 

 as the coast of England — unless the relative levels have since greatly altered. 



It is probable that when the surface of the high plateau is more thoroughly 

 examined, even more recent deposits may be found on it, and if care is not taken 



