provisionally an independent classification; but wherever possible it is better to use for 

 all strata the same standard, and the one having the widest possible application. 



The greater part of the delta*deposits of the high plateau are unfossiliferous ; but 

 as already mentioned thin clays have been found on at least two different levels, and 

 there may be others above or below. The principal clay^deposits are exposed at the 

 foot of, or low down in, the steep scarp overlooking the Maas. Towards the northern 

 end of the high plateau, at Wylerberg, near Nijmegen, there is however a clay*pit high 

 up on the plateau. But the clay*beds ,are nearly vertical, and may have been driven up 

 from a lower level by the thrust of the ice*sheet, which here was stopped by the scarp. 

 The locality happens to be exactly at the limit of the ice, and in England, where for 

 long distances the ice impinged against the rising land, such upthrusts of low^lying 

 strata are common. Messrs. Fliegel and Stoller have published a list of plants from 

 this locality. We have not examined the specimens, but the presence of Vitis and Ptero= 

 caxya. suggests that the clays may be of the same age as those of Tegelen. 



Owing to the position of the main claysbeds, which lie some distance down in 

 the delta sands, they are usually only to be seen near the foot of the scarp overlooking 

 the plain of Dutch Limburg. Thus the fossiliferous strata from which most of the plants 

 are obtained, though lying partly on the Netherland and partly on the Prussian side 

 of the frontier, are only readily accessible from the Netherland side, and the clays there 

 dug are made into bricks in the neighbouring Dutch villages. Whether they are found 

 on the Netherland or Prussian side the claysseams are continuous, and cannot be treated 

 of separately. Thanks to the courtesy of the Prussian Geological Survey we are enabled 

 to deal with them in this Memoir independantly of the political boundary. 



Much has been written about the gravels of the high plateaus of the Maas and 

 Rhine, and they have been accepted by most writers as Pleistocene; though some 

 geologists have recognised that they may include strata of older date. The discovery of 

 various fossiliferous masses of clay and lignite has now taught us that the deposits are 

 composite, and belong to more than one stage, some extending back at least as early as 

 Middle Pliocene. Much remains to be done before the geology of this ancient delta is 

 thoroughly understood ; for at present we only know the fossils of two of its stages in 

 this region, and of a third stage in England alone. 



In this Memoir we will not attempt to deal with the whole of the delta deposits; 

 it will be better to confine our attention to those parts we have more particularly studied. 

 But before passing on to the local evidence, a word of caution is needed to those who 

 attempt to correlate the gravels with terraces higher up the valleys. We are dealing 

 with a river under somewhat abnormal conditions. When geologists examine ancient 

 river*deposits they almost invariably assume that the highest terrace is the oldest; and 

 such is usually the case in a river*valley in a mountainous country, and under normal 

 conditions. But in the case we are now considering the conditions were not normal. 

 A deltasfan was being accumulated to a great thickness, and its further edge was being 

 gradually pushed forward, till it reached the Norfolk coast, 300 kilometres away. How 



