1913] SOME CLAY DEPOSITS IN THE S.-E. PART OF NORWAY 27 



berg-division of the Søreng stage. In this last mentioned division, 

 however, we meet with another series of characteristic fossils 

 especially represented in the rather rich occurrence of Area 

 glacialis, forma typica as observed in the sections of Søreng, 

 Skiptvet, Spydeberg and Berger. In connection with this last 

 mentioned series of fossils we ought rnore specially to call at- 

 tention to the interesting occurrence of Siphonodentalium vi- 

 treum which species had appeared already during the Ra-stage 

 period as is proved in its occurrence at Fjeldly (Moss) and which 

 type is also traced in the lower part of the Rakkestad section 

 and further on in the sections of Søreng and Skiptvet. It is of 

 a great stratigraphical importance, however, that the rather rich 

 occurrence of the Area glacialis- series in the deposits of the 

 Sveneng intraglacial stage is also connected with the common 

 appearance of Siphonodentalium vitreum (P. A. Øyen: The 

 Quaternary Section of Foss, 1913). This fact proves the con- 

 tinuity of deposition from, at least the Ra-stage period to the 

 Sveneng period as no biological interruption has tåken place in 

 that interval of time. 



Continuous, however, as was the deposition during the lapse 

 of time just mentioned no difference in that respect seems to 

 have prevailed as to deep-water deposits quite down to the end 

 of the Portlandia- stage. Consequently, it is not easy to separate 

 the respective layers of the intervening stages in which deep- 

 water deposition has been rather slow and, of course, the thick- 

 ness of the layers in question relatively only small. Animal life 

 on sea-bottom was not roused to any high degree or rapid rate 

 of evolution and consequently we meet with nearly the same 

 character of sea-bottom life in greater depths during a series 

 of stages or periods. We may, however, designate a certain 

 group as an intermediate one and characteristic of the stages 

 just mentioned. And, as such a series may be regarded that 

 which is represented by Abra longicallis. We may trace this 

 series through the sections of Søreng, Spydeberg, Holsbækken, 

 and quite the same fact are met with also in the Valley of 

 Aker or the surroundings of Christiania itself as for instance 



