Recent Sinking of Ocean-level. 249 



lengthened stand of the sea along the Maine coast at a level nearly 

 20 feet higher than the existing high-tide level. 



The similarity of levels for the lowest terraces in areas so widely 

 separated as the Maine coast and the Gulf of St. Lawrence, and the 

 failure of the 300 -mile Micmac terrace to show a distinct tilt, 

 although it runs athwart the isobases of post-Glacial uplift, are both 

 difficult of explanation by assuming crustal uplifts. Confidence 

 in the alternative hypothesis of a eustatic shift was greatly increased 

 by 1919 studies of shorelines in Samoa, about 7,000 miles from the 

 St. Lawrence. 



Samoa. — Mayor had already found wave-cut rock-benches, about 

 8 feet above high tide on all sides of Tutuila, the largest island of 

 American Samoa.' The island is 16 miles long. At its eastern end 

 is Aunuu Island, and about 60 miles farther east is Tau Island of the 

 Manua sub-group. The writer found very fine wave-cut benches 

 at 8 to 10 feet above high tide on Aunuu and Tau, and others at 

 the same general elevation on Olosega Island, 7 miles west of Tau. 

 The distance between the most widely separated benches is 75 miles ; 

 nowhere in that long line did the bench crests depart essentially 

 from a constant level. Explanation by local uplift was at once seen 

 to be highly improbable, for crustal upilift of such uniformity is 

 unknown to geology. 



Eight or ten feet of bench elevation does not, however, measure 

 the total of recent emergence in Samoa. At several points in Tutuila 

 large sea-caves were found. Their floors varied in height above 

 high tide, from 14 or 15 feet at their mouths to 25 feet at the back 

 walls of the caves. Many caves of similar forms and cut in similar 

 rocks are being made by the surf of the jDresent day. The lower 

 lips of the newer caves are characteristically 4 to 6 or more feet 

 below high-tide level, and the floors rise inwards to heights of a 

 few feet above high tide. Hence the emerged caves were cut when 

 the sea-level was nearly 20 feet higher than now. That assumption 

 also explains the 8 ft. benches, for the cliffs now being cut on the 

 Samoan headlands (where not protected by coral reefs) have regularly 

 about 12 feet of water directly at their feet during high tide. The 

 writer fully agrees with Mayor's conclusion that reef corals were not 

 living on any of these Samoan shores "i^hen the emerged caves 

 and benches were developed.^ Hence the reefless, or nearly reefless, 

 headlands of the present time are those where the relation between 

 sea-level and bench-level of the earlier period is best determined. 

 It may be added that no evidence of a negative shift of sea-level 

 greater than about 20 feet could be found in the Samoan Islands. 

 If they ever were submerged more deeply, the evidences have been 

 removed by erosion. 



The equivalence of the negative shift of sea-level in Samoa and 

 along the east coast of North America is shown not only by its 



1 A. G. Mayor Proc. Nat. Acad. Sci. vol. iii, 1917, p. 523. 



2 Ibid., p. 522. 



