seem still to be in progress, and an important subsidence over wide areas appears to 

 have taken place as recently as Neolithic times, probably about 3500 years ago. We here, 

 however, need only deal with the Pliocene delta, which probably began to form as soon 

 as the Diestian, or Lower Pliocene, sea became shoal. Unfortunately however, it has 

 not yet been possible to prove by vertical superposition the exact relation of the delta* 

 gravels to the marine Pliocene strata of Limburg. They occupy slightly different areas; 

 but the underground structure suggests that the oldest delta*gravels are either contem* 

 poraneous with, or somewhat newer than, the marine Scaldisian. The gravels commonly 

 rest directly on Miocene strata; but some boring or mine*shaft may at any time prove an 

 extension of the Pliocene marine strata into the area with which' we are now dealing. 



It being at present impossible to prove the age of the Pliocene delta*deposits by 

 direct superposition, we must fall back on the evidence yielded by the included fossils 

 and the climatic conditions they indicate. Provisionally we must still use two parallel 

 classifications, the one for the marine the other for the freshwater strata. This is the 

 more necessary owing to the exceptional character of the Pliocene floras of the high 

 plateau. We have no similar floras elsewhere in Europe to compare with them, and 

 the older of the two fossiliferous horizons yields nothing but plants, and a few fresh* 

 water mollusca not yet determined. Fortunately the upper or Teglian clays yield, in 

 addition to the plants, certain mammalian remains, and these show a striking resem* 

 blance in part to the Norwich Crag, in part to the Cromer Forest*bed. The position of 

 these two divisions is perfectly well known, for in both cases they yield marine mollusca 

 of Upper Pliocene date. We may safely say that the Teglian is newer than the upper 

 marine strata, or Amstelian, and probably represents the Norwich Crag of England — 

 a stage not yet recognised among the marine strata of Belgium and the Netherlands. 

 The Teglian fauna and flora both suggest a date somewhat earlier than Cromerian, but 

 not older than the Norwich Crag. 



With regard to the earlier stage, represented at Reuver, Swalmen, and Brunssum, 

 this contains a flora of older type, though many of the plants are common to the Teg* 

 lian. They show a somewhat warmer climate and indicate a distinct stage, which we 

 call Reuverian. Their most probable position seems to be Middle Pliocene. They may 

 fill the gap which occurs between the warm*sea deposits of the Scaldisian and the colder 

 sea Amstelian, though no fluviatile deposits have yet been discovered between these 

 two marine divisions of the Dutch and Belgian plain. Provisionally, however, we can 

 only class the Reuverian as Middle Pliocene, leaving its exact equivalent for future 

 determination. 



We must admit the great difficulty of comparing marine faunas with land floras. 

 Even in the same region the temperatures of land and sea do not correspond, and in 

 the case of the ancient deposits of the North Sea basin we are confronted with a special 

 difficulty, as was pointed out when we described the Pliocene deposits of Norfolk. The 

 same deposit may yield contemporaneous subarctic marine mollusca, southern fresh* 

 water mollusca, and plants still living in the same latitudes. 



8 



