418 barrell: movements of the strand line 



Somewhat similar evidence is found, on the shores of north- 

 western Europe, of land emergence above the present level 

 involving regions beyond the limits of glaciation and occurring 

 in a warm stage following the retreat of the ice. Submergence 

 to a level a little below the present stand of the sea then took 

 place. This is presented in comprehensive form by W. B. Wright, 

 of the Geological Survey of Ireland, in his recent book on the 

 Quaternary Ice Age. Wright considers the breadth of this move- 

 ment as indicative of a general lowering of sea level, possibly 

 by a recrudescence of the Antarctic ice-sheets, but either of two 

 other hypotheses is preferable. 



One of these is that the movements represent a diastrophic 

 cycle entirely unrelated to glaciation. The other hypothesis 

 is that the weight of the ice-sheets caused crustal depression 

 directly below the load, but moderate elevation in a wide zone 

 beyond. Upon the removal of the ice-load the first isostatic 

 upwarping carried up higher this marginal upwarped zone with 

 it. This broad regional movement carried it up to a level where 

 it became unstable and a slow settling-back occurred as an af- 

 ter-effect. The close association of these movements with the 

 close of glaciation appears to favor a genetic connection with 

 deglaciation. 



Possible effects of radial shrinkage. Calculations made by the 

 writer as to the quantitative effect of earth shrinkage in pro- 

 ducing an increased speed of rotation, and consequently a rise 

 of ocean waters toward the equator and a depression in the 

 polar regions, suggest that it may be a very real factor. A 

 shrinkage of a mile, if taken up wholly by adjustment of ocean 

 level and not by internal earth adjustment (a supposition which 

 can be true to only a limited degree), would raise the water 

 level at the equator about 35 feet and depress it at the poles about 

 60 feet. 



Such great folding and thrusting movements as have occurred 

 in the later Tertiary suggest that earth shrinkage is an impor- 

 tant factor. Schuchert has called attention id the greater 

 persistence of equatorial epeiric seas and the readvance of waters 

 more frequently from lower toward higher latitudes. It is pos- 



