164 N. S. SHALER — EVIDENCES AS TO CHANGE OP SEALEVEL. 



from the conclusion tha^heir insulated character is of relatively recent 

 date. 



Along the north shore of Europe we find the same evidences of repeated 

 oscillations, with an excess of recent subsidence, Avhich are exhibited on 

 the eastern shore of North America. In both instances submerged forests 

 of recent species appear to indicate that the last considerable movement 

 was one of downgoing. 



Northern Mediterranean Shore. — Along the northern shore of the Medi- 

 terranean the topographic features seems to me to indicate an excess of 

 subsidence. Although some of the islands along the coast may have their 

 separation explained by differential warping or by marine erosion, there 

 are many which can only be satisfactorily accounted for by the hypothesis 

 of recent changes of level of the sea, and this for the reason that the 

 valleys which part them from the mainland are narrow, river-like in their 

 form, manifestly not due to marine erosion and not in a field where we 

 can assume that to glacial wearing was due their segregation from the 

 mainland. 



Islands of the Pacific Ocean. — The evidence of marine changes of level 

 afforded by the islands of the wide seas is not yet in shape for discussion. 

 Such as it is, however, it appears to me to point to the conclusion, one of 

 much importance, that the bottoms of the thallassal areas are now under- 

 going a process of warping which is sometimes downward and sometimes 

 upward. Thus in the Pacific ocean some of the coral islands, by the 

 great depth of water about their bases, lead us to believe that the region 

 in which they lie is undergoing subsidence, while in other areas the con- 

 trary movement is indicated. In the time to come we may hope that a 

 careful study of the evidence afforded by the islands which rise from the 

 deep seas may enable us to chart in a general way, at least, some of the 

 swa3dngs which in recent times have affected in greater or less degree 

 the bottoms of those areas. 



Conclusions. 



The foregoing considerations, though giving but an outline sketch of 

 the problems connected with the changes of level in sea and land, appear 

 to me to afford an extension of our conceptions concerning the conditions 

 which determine the positions of coastlines. 



It seems to me to be evident that the position of a shoreline at any 

 time and place is determined by an exceedingly complicated equation, in 

 which there enter as factors not only the positive up-and-down move- 

 ment of the area of the lithosphere on which the coast lies and the axial 



