( 140 ) 
Geology. — “Cambrian Erratic-blocks at Hemelum in the South-west 
of Frisia.’ By J. H. Bonnema. (Communicated by Prof. 
J. W. Morr). 
To the East of Molkwerum, a railway-station between Leeuwarden 
and Stavoren, stretches a region that from a geological point of view 
is very remarkable; as was especially shown by the interesting 
researches of Dr. VAN CAPPELLE. *) 
The road first leads in a North-eastern direction to the village of 
Koudum, which is situated on elevated ground. As far as here the 
surface showed alluvial clay only; now we see for the first time 
diluvial formations. The outer part of this elevation consists of 
boulder-clay, whereas in two sand-pits it may be easily observed 
that preglacial layers form the inner part. 
A little farther on, when the alluvial grounds are reached again, 
one comes to the Galama-dams. They are found on the Morra, 
according to the above-named author a bottommoraine-lake. 
About a mile farther upward we again find diluvial soil, and on 
continuing our journey in the direction of Rijs we see, just before 
leaving Hemelumer-Oldephaert and Noordwolde, and entering the 
domain belonging to Gaasterland, in a meadow to the right of the 
road a large pit 8 metres deep. From this pit for some years 
boulder-clay has been dug in behalf of the brick-works of the Comp. 
IGaasterland”’, at a short distance, on the other side of the road. 
As far as I know, these are the only brick-works in the Northern 
part of the Netherlands, where bricks are made of boulder-clay. 
The boulder-clay, which forms a bottom-moraine here and which 
must be found very deep in the earth, is coloured blue-grey. Only 
quite near the humus-layer it has become red-brown, under the influence 
1) Van Carpeue, Les Escarpements du ,Gaasterland” sur la côte meridionale de 
la Frise. Extrait du Bulletin de la Société Belge de géologie, de paléontologie et 
d'hydrologie 1889. 
Van Cappette, Bijdrage tot de kennis van Frieslands bodem. II. Eenige mede- 
deelingen betreffende de Gaasterlandsche kliffen. Tijdschrift v. h. Koninkl. Nederl. 
Aardrijksk. Genootschap. 1890. 
Van Cappette, Bijdrage tot de kennis van Frieslands bodem. IV. Eenige mede- 
deelingen over de diluviale heuvels in de gemeente Hemelumer-Oldephaert en Noord- 
wolde. Tijdschr. v. h. Kon. Nederl. Aardrijksk. Genootschap. 1892. 
Van Carperre, Bijdrage tot de kennis van Frieslands bodem. V. Karteering van 
't diluvium van Gaasterland en Hemelumer-Oldephaert en Noordwolde. Tijdschr. v. 
h. Kon. Nederl. Aardrijksk. Genootschap. 1895. 
Van Cappetie, Diluvialstudien im Südwesten von Friesland. Verhandelingen der 
Koninkl. Akad. v. Wetensch. te Amsterdam. 1895. 
