260 Professor Daly — Recent Sinking of Ocean-level. 



Cause op the Eustatic Change. 



Before the fact is established it would be idle to dwell overmuch 

 on the explanation of a 20 ft. drop in ocean level. If lands in both 

 hemispheres, in high and low latitudes, emerged simultaneously 

 and to a nearly equal amount, the cause of the emergence cannot 

 be found in a change in the earth's centre of gravity nor in a change 

 in the speed of her rotation. There is no evidence compelling belief 

 that the ocean basin has been so enlarged in recent time as to cause 

 a negative 20 ft. shift of sea-level. More hopeful is the hypothesis 

 of an increase in the volume of existing, non-floating glaciers, an 

 increase taking place a few thousand years ago. If the Antarctic 

 ice-cap were then thickened to the average amount of about 700 feet, 

 an average sinking of sea-level to the extent of nearly 20 feet would 

 be inevitable. 



In favour of this suggestion would be evidence of a worldwide 

 oscillation of climate, like that which seems to have affected the 

 Christiania region in Recent time. If the whole earth was in the 

 Tapes period a little warmer than now, less water may have then 

 been taken from the ocean to build the ice-caps ; sea-level was a 

 little higher than at present. The oscillation as a whole would be 

 but an incident in a series of climatic changes which began with 

 the" opening of the Glacial period. 



Conclusion. 



The facts on which the hypothesis of a general post-Glacial fall 

 of sea-level is based belong to three groups. 



Because of the recency of strand lines now about 20 feet above 

 high-tide level, many of these lines should not have undergone 

 important deformation, and if their emergence was due to the eustatic 

 shift their accordance of level should be observable. Notwith- 

 standing the difficulties attending a canvass of the world's coast- 

 lines, a comparison of published observations seems to show that 

 the speculation will bear the test of a fuller induction founded on 

 special field work. 



Naturally less troubled by the danger of subjectivity, the con- 

 clusions drawn from a study of the Micmac terrace or the lowest 

 coastal-j^lain terrace to the southward of New York City are now 

 perhaps more compelling. Practical uniformity for the terrace 

 level along 300 miles of coast in the one case and along nearly 

 1,000 miles of coast in the other is certainly not expected on the 

 uplift hypothesis, which likewise does not easily explain the 

 strikingly accordant levels of Samoan benches at points only 75 

 miles apart. 



A third group of facts, relating to the necessity of synchrony for 

 the different strands abandoned by the sea, is meagre, but so far as 

 it goes this evidence permits the main hypothesis, and its analysis 

 suggests methods for future research. 



The combination of all three groups of observations is much 



