( 31i) ) 



of (listiirhance ; vi/. tlio fonnci- lius ils foei near the nierklians 

 of uoon and iiiidiii'ilit, tlio lalfer near llio line of separation of day 

 and iiigiit. 



Tlic axis ai'ound \\ liieli llie Held of diytnrbanee revolves is so 

 neai'lv eoineideiit willi the magnetic axis of the eai-th, that it seems 

 the field is caused by any emanation from tiie,sun, deflected by the 

 earth-magnet acting as a whole, and not by the surface distribution 

 of terrestrial magnetic force. 



Full accouni on this research will be soon gi\en in the Xalniir- 

 kiuulig Tijdschrift \oor Nederlandscli-lndië. 



Geology. — "A piece of Liiii('-stoii<> of the cci'rt/opi/ifc-zone from 

 tke Dutdi Dilurhnn.'" l>y .1. H. Üonnkma (Coinniuiiicated 

 by Prof. ïMartin). 



In a few papers which a short time ago appeared in these reports, 

 I communicated some particulars of the Camltrian erratic blocks 

 from the loam-pit near Hemel uni; this time I intend to treat of the 

 Under-silurian ones. 



First of all, however, I wish to add something to my information 

 concerning the way in which Under-cambrian sandstone Avith Disci- 

 nella Holsti Moberg is spread. I tlien ^) said that I had not been 

 able to find anything certain, in German literature, about erratic- 

 blocks of this stone. This was a consequence of my sources of 

 information on sedimentary erratic-blocks being ineomi)lete. After my 

 I>aper had ai)peared, Prof. Stollky ^) was so kind as to send me 

 an essay that had seen the light already a few years before, in which 

 the occurrence of this kind of erratic-blocks in the German diiiniuni 

 is uiade mention of. 



No more did 1 find, here in the Hemelum loam-))it, the opinion 

 confirmed expressed i. a. by Staring ■'), Martin ') and Sciirokdkr van 

 UKR KoLK ^), that Under-silurian erratic-blocks were almost entirely 



1) BoxNEMA, Some new Uiidcr-cainbrian errulicblocks from Lhe UuUh Diluvium. 

 Pioc. Royal Acad. Amsterdam. Vol. V (1903) p. .oGl. 



~) Stolley, Einige none Sedimentart;'cscliiehe ans Sclileswig-Holslciii mid bonafli- 

 haiicn Gebieten. Scluil'lcn dcs Xaliuwissenscbafllichon Voicmiis fiir Scldcswig- 

 Holslein. 1898. 13d. XI. p. 133. 



=5) Staring, Do bodom van Nederland. 1800. II. p. 99. 



•') Martin, Nicileilandiscbe und Nordwesldeulsciie Sedimeiilargescliiebe. 1878. 

 p. li. 



■') ScHiioEDER VAN DER KoLK, Bijdrage tot de kennis der verspreiding onzer 

 kriilallijne zwervelingen. Dissertatie. 1891. p. .j1. Stelling VU. 



