318 Reviews — Dr. W. C. Brogger — 



history of their country. This circumstance moved Professor 

 Brogger, although, in his own estimation, no specialist in the field 

 of glacial geology, to trace out in detail the important series of 

 changes which accompanied and followed the retreat of the last 

 great ice-sheet which covered Southern Norway. Nowhere are the 

 records of these changes better preserved and more clearly shown 

 than in the districts bordering the Christiania fjord, a region which 

 the author has already made classical by his well-known description 

 of its Palaeozoic geology and fossils. 



Although the title of the work refers to the changes of level 

 which the country has undergone in the period under consideration, 

 the evidence of these, to a great extent, is furnished by the 

 characters of the molluscan fauna in the various deposits, and the 

 work gives mainly the results of a detailed study of the changes 

 which have taken place in this fauna by the introduction of certain 

 species and the disappearance of others. Not only changes of level 

 but modifications of the climate are also indicated by the various 

 phases of the molluscan life which flourished in the Christiania fjord 

 after the retreat of the ice-sheet. 



The author treats the subject under three main divisions or 

 periods. The first of these — the period of subsidence — begins at 

 a time when the front of the glacier extended across and on both 

 sides of the southern portion of the Christiania fjord, and in front of 

 it huge terminal moraines were being formed beneath the sea-level, 

 while outside of these the Yoldia-clays were laid down. The level 

 of the land at this time was not much lower than at present, but 

 a movement of depression had set in which continued until the land 

 had sunk to the extent of about 240 metres (787 feet), and the sea 

 margins reached to the southern end of Lake Mjosen and the other 

 lakes of Central Norway. During this sinking interval the land-ice 

 was gradually melting back northwards, leaving behind, at 

 successive stages in its retreat, huge ramparts of terminal moraines 

 indicating prolonged pauses in its recession. Over the areas vacated 

 by the ice, beds of shelly clays were deposited ; the shells for the 

 most part are of Arctic species, but in the later stages of the 

 depression there was an admixture of boreal forms. 



The second period was ushered in by a movement of elevation, 

 and its various stages are shown by the abundance of shelly sands 

 and gravels at different levels above the sea, and to a subordinate 

 extent by clay-beds as well. 



The third, or post-Glacial period, commences about the middle 

 of the elevatory stage and continues to the present. It is 

 characterized mainly by shallow-water sands and gravels, with 

 numerous shells and clay-beds as well. The mollusca are now for 

 the most part boreal, and southern forms and the principal Arctic 

 species have disappeared. 



I. The Period of Subsidence. 

 Eeturning now to the late Glacial period of subsidence, the author 

 states that the terminal moraines — or ras, as they are designated — 



