236 



therefore may be estimated to be of Lower-Oligocene date; at all 

 events thej must liave been formed at the commencement of the 

 Oligocene transgression. 



These formations are best compared with the Oligocene phosphatic 

 deposits of the North-German Plain, of which those from Helmstedt 

 have become familiar to us through the researches of Von Koenen 

 and H. B. Gkinitz '). It appears that all the fossils found in Twente, 

 ex(!ept Oxyrphina Desori, are also to be found near Helmstedt, 

 wliicii proves tiiat tiie two deposits are equivalent. 



This induces me to [)nt forward some remarks about the forma- 

 tion of phosphatic nodules. Most authors advocate the view that 

 the more or less rounded shape of these bodies is to be attributed 

 to transportation, which view is adhered to bj recent observers, 

 as shown by the "Eindrapport" from which we just now quoted a 

 passage. We contend that the nodules, in many cases, are not 

 rounded, but more or less irregular, nay, as Staring ') observes, 

 they often seem to be made up of two or more rounded nodules. 

 The shark's teeth are in many cases enclosed in an approximately 

 rounded phosphatic nodule: the portion that is sticking out, however, 

 is not worn oft' at all, which fact clashes with the presumable 

 genesis. H. B. Geinjtz assumed the transport of the nodules to have 

 taken place in (he Recent Tertiary and based this view on the 

 fact of their presence in the layers of Myliobates and of Larana 

 cuspidata, which he had examined, and which up to that time had 

 been recognized only in the Pliocene. Now, this cannot apply to 

 the Overijsel phosphatic deposits, in which these remains have also 

 been met with, because the younger deposits of the Oligocene also 

 occur hei'e. The palaeontological argument that the rounded shape 

 is attributable to rolling cannot be sustained. We are bound to 

 assume that after the formations of the phosphate-concretions, the 

 position of the deposits remained unaltered, which conception has 

 been supported already by Dr. W. P. A. Jonker ') on other grounds. 



I wish to conclude by gratefully acknowledging my indebtedness 

 to Mr. J. Bernink, Director of the Museum "Natura Docet" at 

 Denekamp, for granting me access to the fossils collected by him. 



1) H. B. Geinttz, Die sogenannten Koprolietlienlager von Helmstedt, Biidden- 

 stedt und Sclileweke bei Harzburg. Abliaiidlungen der Naturwiss. Geselschaft ,Isis" 

 in Dresden. 1883, p. 3-14. 



H. B. Geinitz, Ueber iieue h'unde in den Phosphatlagern von Helmstedt, Bud 

 denstedt und Schleweke. Isis, 1883, p. 37 — 46. 



2) W. H. C. Staring, De bodem van Nederland. 2e deel. Haarlem, 1860, p. 195. 

 ') W. P. A. Jonker, Het ontstaan van phosphorieten. Handelingen van het 17e 



Natuur- en Geneeskundig Congres, 1920, p. 94—96. 



