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If we only had at our disposai the data mentioned by 

 Van Eeden, we would not be able to bring the pro- 

 blem, which interests us hère, much nearer to its solution. 

 Fortunately, however, there are other plants to be men- 

 tioned, many of which are much more typical as compa- 

 nions of our rivers and give us much more évidence too 

 in favour of an ancient Rhine-bed past Harlem to the 

 north, such as those mentioned byVan Eeden, and 

 which are of greater value to us for the solution of the 

 problem. In connection herewith it must be pointed out, 

 that it is generally accepted, that during the oak-age 

 there has been a period of spécial dryness and warmth. 

 Big ranges of wood should hâve perished in those times 

 and a distribution of plants set in from the coast of the 

 Black Sea in the direction from south-east to north-west 

 to our régions, and specially so through the valleys of 

 the Danube, Main and Rhine, as the steep slopes of thèse 

 river-valleys offered favorable passages, which were free 

 from woods. Actually thèse plants, représentatives of the 

 so-called pontic-pannonic plantcommunities, are only 

 found hère in very warm places and as a rule they give 

 unmistakable indications concerning the course of the 

 big rivers. The examples which are best known are the 

 following : 



Silène Otites Smith ; in our country this species only 

 grows on the inner side of the dunes, further near Huizen 

 (mouth of the river Vecht) and finally in one place corres- 

 ponding to the German stations, namely on the isle of 

 Schiermonnikoog ; it is not found in Belgium ; 



Artemisia campestris L., growing in our country strictly 

 along the big rivers and in the environs of Harlem near 

 the ancient Rhine-bed of Van Eeden; in Belgium this 

 plant is only found in a few places in the vicinity of the 

 Meuse ; 



Eryngium campestre L., occurring e. g. on the Kyffhâuser 



