Glacial Changes in Christiania. 321 



The extensive areas between the outer and the inner ra are covered 

 by thick deposits of clay which rest directly on the striated surfaces 

 of the older rocks. Only a scanty fauna of about a dozen species, 

 most of them of a high Arctic character and similar to those in the 

 lower Area-clays, are known from these beds, which are termed 

 the middle Area-clays. The principal forms are Area glacialis, 

 distinctly smaller than those in the lower beds, and Portlandia 

 leiiticula. These middle Area-clays are now at levels of 150 metres 

 above the sea ; they indicate a further sinking of the land during 

 the withdrawal of thq ice from the outer to the inner ra. 



From the inner ra at Svelvik the glacier melted back northwards 

 to the valleys of Drammen, Lier, and Christiania, where the third 

 stage in its retreat is marked by terminal moraines, similar to those 

 lower down, most of which served to dam up lake-basins behind 

 them. In the districts vacated by this stage of the ice retreat, 

 Brogger has recognized a clay deposit of deep-water origin, the 

 younger or upper Area-clay, in the lower parts of the valley, up to 

 about 120-130 metres above sea-level, containing thirty-seven species 

 of mollusca, and somewhat higher, at levels up to 175 m., a clay of 

 a somewhat shallower character, named the younger Portlandia-clay. 

 The fauna of the younger Aroa-clay is not, like that of the older 

 Yoldia-clays, of a purely Arctic character, for only about half the 

 species in it are now living in the Kara Sea ; it contains an admixture 

 of boreal species, and it corresponds with that now existing at depths 

 of 100-200 m. off the north coast of Norway. 



The further withdrawal of the ice northwards is marked, as hitherto, 

 by moraines at intervals where pauses have taken place ; the fourth 

 of these occurs behind the clay terrace at Lillestrommen, and a fifth 

 at the south ends of the large lakes of Central Norway — Mjdsen, 

 Hurdalsvand, Eandsfjord, etc. At this fifth or epiglacial station, 

 as it is designated, enormous masses of clay, and upon these to the 

 north, sands and gravels, are spread over the terraces of Komerike 

 and part of Riugerike. These gravels appear to have been all laid 

 down beneath the sea; they are now about 225 metres above sea- 

 level. But few mollusca are found in the clays between the third 

 and epiglacial moraines ; the principal species are Portlandia lenticula 

 and Astarte compressa, and the beds are named after the first 

 of these. 



One of the most striking phenomena of the period of the greatest 

 submergence in the Christiania fjord is the well-known coral reef, 

 so carefully described by M. Sars, consisting of masses of the deep- 

 water coral Lophohelia prolifera, Linn., which, in a dead but well- 

 preserved condition, occur at Drobak, south of Christiania, covering 

 the sea-bottom at levels of 60 metres below the surface, and they 

 are also found over an ai'ea of about 100 square kilom. to a height 

 of 30 m. above the sea. Associated with the coral is the giant form 

 of Lima excavata, Fabr. Both the coral and shell are now found 

 living in the Norwegian fjords at depths of 100-300 fathoms, 

 and it is probable that they existed in the Christiania fjord at 

 a depth of not less than 150 metres, when the climate was not very 



DECADE IV. VOL. IX. — NO. VII. 21 



