( 101 ) 



2'"'. From liis observations Dibois luis ctilculated that about Y,. of 

 the Aohime of the boulder-sand bed lias consisted of boulders and as 

 in that region boukler-cUxj is very poor in stones, boulder-elay of 

 enormous tliiekness must have been washed out. 



I have not repealed this computation, ImiI have I his objection that 

 I have often observed that the percentage of stones in the boulder- 

 clay — which indeed is very diflerent in various places ^ — increases 

 very much towards the surface. The ret(uired thickness would decrease 

 very much by it and as we know so little about the original thick- 

 ness of the gi'ound-moraine, this reasoning does not seem to me to 

 settle the question. 



3"l "The boulder-sand contains very little flint, the boulder-clay 

 very much, everywhere. Flint is the kind of rock most frequently 

 occurring in the clay (Odoorn, Zwinderen, Nieuw-Amsterdam, Mir- 

 dumer Klif, Nicolaasga, Steenwijkerwold, Wieringen, etc.)." 



First of all the remark that the places outside the Hondsrug, 

 mentioned here had better not been taken into consideration. As 

 regards the Hondsrug the decision that flint in boulder-cla}^ is the 

 prevailing rock is in its generality no doubt wrong. In clay of the 

 Hondsrug in Groningen Hint is very rare indeed. For example: When 

 a pit, about 27^ M. deep and a diameter of 3 M., was dug in the 

 garden of "Klein-Zwitserland" near Harendermolen (the soil consists 

 there chiefly of clayish sand and sandy clay, but with very much 

 limestone), there was not a single flint among some thousands of 

 lK)ulders which were protluced ! This is, less strictly taken, every- 

 where the case there. In the Hondsrug in Drente I found some more 

 flint in various clay-pils, but it was never predominant. Moreover 

 through the disappearance of limestone the percentage is doubled. 

 In this respect the Hondsrug difTers very much from other parts of 

 our glacial diluvium and this in my opinion very interesting cha- 

 racteristic will have to be explained saiisfactorily. — To mention 

 also some observations outside the Hondsrug which argue the 

 reverse : the boulder-sand e. g. near Roden is exceedingly rich in 

 flint, as it is in Steenbergen, etc. 



This flint therefore does not prove anything. 



4'''. "Even the deepest and evidently not washed out parts of the 

 boulder-sand, which rest immediately on the Rhine-sand, are as a 

 rule poor in clay." 



I do not know what enables Dubois to state that they are not 

 washed out. I beg to remind the reader of the vanished lime-stone 

 it contained and the numerous brown veins sometimes as thick as 

 an arm, which occur mostly under the boulder-sand in the white 



