T. F. Jamieson — Changes of Levelin Glacial Period. 485 



affords a happy means of explaining this curious and later pheno- 

 menon also. 



The depression of a large tract of land by a weight laid upon it 

 would almost of necessity be accompanied by a corresponding rise 

 in the region lying immediately beyond. We see this on a small 

 scale when we push down a hollow in an elastic substance, or when 

 a depression of the soil is caused by the advance of a heavy mound 

 such as a railway embankment, which leads to a bulging up of the 

 ground immediately in front. The depression of the ice-covered 

 area of Scandinavia would therefore probably produce a similar 

 bulging up of the outer region, and thus close the Cattegat and 

 block out the sea from the entrance to the Baltic, thereby converting 

 it for a time into the state of a fresh-water lake. This would happen 

 probably after the Baltic glacier had shrunk considerably, and it is 

 just then that the fresh-water condition seems to have occurred. At 

 an earlier period, when the Scandinavian ice spread far and wide, 

 the bulging up would take place at a much greater distance, and 

 would embrace a larger area. Here again we have evidence of 

 a like result, for we know that the southern part of the German 

 Ocean and the Straits of Dover were converted into dry land during 

 an earlier part of the Glacial period ; and that the mammalian fauna 

 of the continent ranged freely over that ground into England. The 

 lower reaches of the Thames too, and other rivers of East Anglia, 

 were also by the same action probably converted more or less into 

 lakes and pools, which appear to have been haunted by the hippo- 

 potamus, whose remains are frequently met with in the valley gravel 

 -and alluvial deposits of that quarter. In the South of England and 

 in Germany there are other proofs of straining and earth-movement, 

 due possibly to the same heavy pressure exerted by the Scandinavian 

 ice, and propagated outwards beneath the surface. Movements of 

 depression occasioned by forces of this- nature must generally be 

 attended in neighbouring regions by strains, fractures, and move- 

 ments of elevation, which are to be looked upon as the natural 

 accompaniment and complement of the depression caused by the load 

 of ice. Here, then, it seems to me we may find an efficient cause 

 for the production of many such movements, in regard to which no 

 explanation has hitherto been offered. 



One of the most obvious changes in the weight of the surface 

 arises from the action of rain, rivers, and glaciers continually wearing 

 and washing down matter into the sea. This incessant degradation 

 must always be wearing away and lightening the mountain regions, 

 so that the tendency in them should be to a slow and gradual rise, 

 whereas on the sea bottom the opposite effect would take place, and 

 there the tendency Avould be to sink. Such action would tend to 

 the permanence of continents, which otherwise would be worn down 

 much faster. Land is laud, I presume, because it is lighter than 

 the area occupied by the sea, and the great mountain regions are 

 probably the least heavy parts of the earth's crust. 



Our ignorance of the state of matters in the interior of the earth 

 is so great that we are not justified in dogmatizing on the subject, 



