1913] SOME CLAY DEPOSITS IN THE S.-E. PART OF NORWAY. 5 



This central section of the district in question might be of 

 some use as a leading one, at any rate, in some respects. The 

 three base-layers of the section are supposed to be found below 

 the water-level of the river, the environments of which are 

 represented in plate I. 



The correlative importance of Portlandia arctica and Area 

 glacialis gave rise to some, controversy betvveen Sårs and 

 Torell. And, on reading the current literature relating to this 

 subject one is inevitably forced vvith the impression that the 

 discussion upon this peculiar phenomenon can not as yet be 

 regarded as settled. 



Hoping, however, that my work just upon this subject may 

 contribute to elucidate to some degree this intricate problem 

 I am going to give a concentrated review of my observations 

 in the field and comparative study of fossils tending to follow 

 as well the geological evolution as the biological development 

 involved with the solution of different questions connected with 

 this very phenomenon. 



The classical locality of Verlebugten at Moss ought to form 

 the starting point. Here Sårs noticed the occurrence of Yoldia 

 arctica, Tellina proxima, Saæicava arctica and Buccinum 

 groenlandicum in a sandy clay deposit mixed with stones. He 

 took it to be a shallow-water deposit of the Lami nåria belt (Foss, 

 Dyrelevn. fra Quartærper. 1864, p. 19). The species determined 

 by Sårs to be B. groenlandicum has on closer inspection 

 proved to be Buccinum terræ novæ. To the list of Sårs some 

 species, viz. Leda pernula Mull., Nucula tenuis Mont, var. 

 expansa, Buccinum hydrophanum Hanck. var. texturata 

 Poss. and Sipho togatus Mørch were added by Brøgger (Sengl. 

 & postgl. nivåforandr. i Kristianiafeltet, 1901, p. 18) who con- 

 cluded that the Yoldia-clay had been deposited in this place at 

 a time when the shore-line was at a level of 20—30 metres 

 higher than at present (1. c, p. 77) and he further on concluded 

 that in the southern part of Norway the deposition of the 

 Yoldia-clay had tåken place almost contemporaneously with the 

 deposition of the large ra-moraine, in some places perhaps a 



