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of the weather. It contains comparatively few erratie-bloeks. They 
often show very fine glacier-scratches and are mostly of average size. 
During the time when this opportunity of gathering erratic-blocks 
has presented itself, I have several times visited, from Leeuwarden, 
this loam-pit. The result of these visits is that I brought home rather 
a large number of erratic-blocks (probably between 300 and 400). 
The sedimentary ones are still here at present; after studying them 
I intend to present them to the Geological Institute at Groningen. 
The others, whose number is small compared with that of the sedi- 
mentary stones, have already been given to this Institute. 
Though my collection is still small, it is large enough to confirm 
my opinion that our knowledge of our sedimentary erratic-blocks 
leaves much to be desired. I formed this opinion already after 
examining the erratic-blocks of Kloosterholt. *) 
In gathering erratic-blocks in the Gron. Hondsrug I had gradually 
come to the conclusion that our sedimentary ones almost exclusively 
originated from Silurian layers, and that the latter must have shown 
much resemblance to those of the Russian Baltic-sea provinces, perhaps 
are still to be found there. ‘On getting acquainted with the erratic- 
blocks in the boulder-clay of Kloosterholt, however, I could not but 
see very soon that at any rate this rule does not hold good in all 
cases. In this place I often found pieces of older and younger forma- 
tions, while corresponding stones occur as firm rocks in Sweden and 
Denmark. The very same phenomena, as I hope I shall indicate, are 
seen in the erratic-blocks of Hemelum. Besides Silurian formations, 
others, both older and younger, are numerously represented. At the 
same time all of them show almost exclusively a West-baltie character. 
We should then see the remarkable phenomenon that at Groningen, 
which is situated between Kloosterholt and Rijs, erratic-blocks greatly 
differ from those of the two places mentioned. 
Gradually, however, I am beginning to doubt whether my opinion 
about the character of the erratie-bloeks in the Groningen Hondsrug 
should be the right one. In the years when I used to gather there, 
digging was atmost entirely confined to the upper layers, so the 
chances are, that deeper parts contain other kinds of erratic-blocks. 
A few facts seem to indicate this. First of all : while a deep cave 
was being dug under the brewery called Barbarossa, at Helpman, 
big blocks of Saltholmlime with Terebratula lens Nilss made their 
1) Van Carker, Ueber eine Sammlung von Geschieben von Kloosterholt. Zeitschr. 
d. Deutsch. Geol. Gesellsch. Jahrgang 1898 p. 234. 
Bonnema, De sedimentaire zwerfblokken van Kloosterholt. Versl. v. d. Koninkl. 
Akad. van Wetensch. te Amsterdam 1898 pag. 448. 
LO 
Proceedings Royal Acad. Amsterdam. Vol. V. 
