( 565 ) 



resembling each other. From llie description van Calker gives of the 

 stonekernels occurring in them, Holm ah-cady drew the conchision that 

 the3' originate from Hyolitlius de Geei-i. Tlicse erratic-l)l()cks consist, 

 however, of dark ascii-grey sandstone, so tliat they differ in colour 

 from the jMurmerwoude ones. 



Afterward two more pieces of Hyolithus-sandstone were mentioned 

 by me ^). One was found at Kloosterliolt (Heiligerlee), the other 

 at Roden, in tiie North of tlie province of Drente. The former is a 

 small piece of tine-grained sand-stone, yellow-grey on the inside and 

 brownisli on the outside, in wliich are found some fragments of 

 stone-kernels of Hyolitlius-sliells. A few of these fragments are enti- 

 rely dark-brown, others huve a light-grey surface. One of the stone- 

 kernels shows tiie transverse section characteristic of Hyolithus de 

 Geeri. The Roden erratic-bh)ck is ratlier a large slab of sandstone, 

 containing especially ott-j>rints of pyramidal Hyolithus-sliells. This 

 one is reddish on the inside and light-grej' on the outside. 



Where the sandstone-layers of which the Murmerwoude erratic- 

 blocks in former times formed })art, were originally Umml as firm 

 rock, cannot be said with certainty, as appears from \vhat was 

 written above. Most probably it was near the western coast of the 

 southern part of Sweden. 



III. That the knowledge of our sendimentary erratics still leaves 

 so much to l)e desired, must certainly be partly atti-ibuted to tlie 

 fact that so few of them have been gathered up to this time. Non- 

 geologists, too, by their researches, may deserve well of this branch 

 of knowledge, as was pro\'ed once more by Prof. Dr. J. C. Kapteyn, 

 filling a chair at the Groningen University. 



This well-known Astronomer, who in summer lives at Vries, in 

 the northern part of Drente, last summer searched the surroundings 

 of this village for sedimentary erratic-blocks. To liis researches we 

 o\ve a piece tiiat is certainly the most interesting of the erratics 

 described here. 



Just outside this village, by the road leading to Donderen, was 

 found a small, slab-shaped erratic-block three centimetres thick, the 

 largest dimension of which is 14 centimetres. It consists of sandstone 

 coloured yellow-grey by ferrihydroxide. At the surface it is brownish. 

 With muriatic acid there is no efferx^escence. The grains of sand 



1) BoNNEMA. De sedimentaire zwerfblokken van Kloüslerliull (Heiligerlee). Versl. 

 V. d. Koninkl. Akad. v. VV^elenscliai^pen 1898. p. 450. 



Van Calker, Ueber eine Sammlung von Geschieben von Klooslerholt. Zeitschr. d. 

 Deutsch. geol. Gesellscli. Jahrg. 1898. p. i234. 



