T. F. Jamieson — Oscillation of Land in Glacial Period. 465 



between glaciation and submergence, by Dr. Penck, of Munich.^ It 

 is foiiuded upon some recent results arrived at by Fischer and other 

 Germ;in mathematicians in regard to the attractive force exerted by 

 continents upon the sea. According to the law of gravitation, every 

 substance in the world attracts every other substance with a force 

 proportional to their masses. A continent of land will therefore 

 exert an attractive influence upon the sea, and cause it to rise upon 

 its shores to a height which will vary according to the mass of land 

 which causes the attraction. On this account it is alleged that the 

 surface of the ocean is not actually that of a regular spheroid, as it is 

 generally supposed to be, but rises much higher upon the borders 

 of continents than it does in mid-ocean. Consequently even in the 

 same parallels of latitude the surface of the sea is not everywhere 

 equidistant from the centre of the earth, but may show differences 

 of level amounting to many hundred feet by reason of this attractive 

 force which the masses of land exert upon it. 



Such being the case, it follows that anything which increases the 

 mass of land will increase its attractive force and cause the sea to 

 rise to higher levels along its border ; and thus a great thickness of 

 glacier-ice laid upon a continent by adding to its mass will draw the 

 water towards it, and thereby raise the sea-level in its immediate 

 vicinity ; and according as the ice increases or disappears, so will 

 the level of the sea rise or fall in proportion. Moreover the altitude 

 of the sea-beach may vary considerably, it is said, along the border 

 of one and the same continent by reason of the varying thickness of 

 the ice in different parts. In this way it is conceived an explanation 

 is found for the fact that in Norway the old terraces and sea-beaches 

 do not coincide in elevation, but vary much in altitude even in places 

 not very far distant from one another. It is therefore maintained 

 that the sea may rise and fall along a coast and yet the old shore 

 lines may be neither parallel nor horizontal. 



The attractive force may be so localized that its intensity varies, 

 and thus the influence of local masses of ice may account, it is 

 thought, for considerable variation of sea-level in places even not 

 far distant from one another. 



These views are certainly somewhat different from those which 

 have hitherto prevailed in regard to the regularity of the sea-level, 

 and it seems to me are founded on an exaggerated estimate of the 

 attractive force. If there is such a great difference in level in the 

 surface of the sea in different places, the barometer should give in- 

 dications of it. It is therefore much to be desired that every means 

 should be taken to ascertain the relative height of the sea in various 

 places calculated to test the accuracy of the views I have mentioned. 



There are, however, some well-known facts connected with the 

 submergence of the land in glacial times which seem to me inex- 

 plicable by the attractive force of the ice, even suppose we should 

 grant it to have been all that is stated. For example, near Dublin 

 shell-beds are found in Wicklow at an elevation of 1200 feet. Now 



' Schwankungen des Meeresspiegels, Jahrb. der Geograph. Gesellschaft zu Munchen, 

 bd. vii. 1S82. 



DECADE II. — TOL. IX, — NO. X. 30 



