( ^30 ) 



over the Hondsrng, a certain elevation of tlie soil underneath it at 

 the same time having taken place from some cause or other. I 

 supposed, as one possibility, the mean pressure of the ice to have 

 been somewhat lessened, or its progress to have been easier just 

 above the present ridge. I imagined the change in the direction of 

 the ice-stream to have been occasioned by the Northern ice-sheet 

 being pushed back by the British ice-sheet in the German Ocean. 



Recently, Dr. H. G. Jonker, one of Prof, van Calker's youngest 

 pupils, has refuted my \'iews in these Proceedings^). Though, from 

 a few lines at the end of his paper, it appears that he agrees with 

 me on the main point, — namely, that, as to its geological compo- 

 sition, the Hondsrug in Drenthe consists of a fluviatile nucleus, 

 covered with a glacial deposit, and that on this account it cannot 

 possibly be considered a terminal moraine. But on the other hand, 

 he advances numerous arguments to disprove the probability of a 

 change in the direction of the ice-stream, and one of the ways in 

 which I conceived the raising of that ridge could have been effected. 



In the first place I wish to refute, as briefly as possible, the 

 objections raised by Dr. Jonker to the explanation of the last-named 

 point suggested by me. 



As mentioned before, the results of my investigation principally 

 related to the portion of the Hondsrug situated in the Southern part 

 of Drenthe, about half of its entire length in that province. I myself 

 mentioned several spots where the glacial covering does not consist 

 of sand but of loam. This circumstance however is not inconsistent 

 with the statement that the ridge, in general, is less rich in claj^ 

 than its Western borderland. Neither does it exclude a freer move- 

 ment of the ice-sheet over the Hondsrug, which 1 suggested as a 

 probable agency in the formation of this ridge. 



As far as I am able to judge from the few excavations I visited 

 in the Northern portion of the Hondsrug, it seems to me that, in 

 general, its structure does not differ from that of the Southern part. 



Dr. Jonker further mentions a few spots in the North of Drenthe 

 where the glacial cover of the Hondsrug consists of boulder-clay, 

 viz. in the neighbourhood of Gasselte and Zuidlaren. Of the latter 

 locality and also of some places near the town of Groningen, where 

 much boulder-clay is found. Dr. Jonker himself says that the hillj' 

 character of the Hondsrug is less distinctly to be recognized, and 

 that the Hondsrug is hardly noticed there. These spots therefore may 

 be left out of account. 



With regard to Dr. Jonker's reference to the borings of the Dutch 



') Vol. VIII (1905), p. 96-104. 



