Recent Sinking of Ocean-level. 253 



may be connected with the difference of datum-levels assumed in 

 the two countries. Ordnance datum in Ireland is 8 feet below 

 Ordnance datum for Great Britain (mean water-level at Liverpool, 

 which is practically the same as in Ireland). In general, 25 feet above 

 Ordnance datum in Scotland means 20 feet or less above high tide, 

 the significant level. 



For a total distance of about 1,000 miles along the southern 

 shores of England, Wales, and Ireland, a " pre-glacial " terrace 

 " has been traced almost continuously ". It occurs also in France, 

 from Calais to beyond Brittany. " Throughout the greater part 

 of this district it stands uniformly some 10 or 12 feet above the 

 present high-water mark, and maintains a remarkable parallelism 

 with the present sea-level. This parallelism proves almost beyond 

 a doubt that no permanent deformation by folding or faulting has 

 taken place over this wide area since pre-glacial times." ' The 

 " pre-glacial " age is deduced from the presence of boulder-clay 

 and early " Pleistocene " fossils on the rock-bench cut when the 

 sea stood at the higher level. Wright holds that the old strand owes 

 its position to a eustatic oscillation of sea-level. 



The progress of discoveries and ideas concerning the lowest 

 strands in the British Isles shows one kind of danger into which 

 a compiler may run if the record of relevant facts is inadequate. 

 Considering the many statements by good observers as to the 

 continuity of the 20 ft. level or of the 25 ft. level all around both 

 Great Britain and Ireland, it would look as if these islands could 

 afiord excellent corroboration of the eustatic hypothesis. When, 

 however, strand-lines of about the right elevation are found to be 

 partly " pre-Glacial " and partly post-Glacial, and when it is further 

 suggested that the later beach-level has been deformed, the difficulty 

 of using the British data is clear. If Wright's view as to the warping 

 of the Neolithic beach (the 25 ft. or 20 ft. beach of Scotland and 

 Ireland) is correct, then the relation of this very extensive strand- 

 line to the eustatic hypothesis could only be established after the 

 dates of the warping and the eustatic shift become known. Meantime 

 the British Isles represent a region where the ascertained facts, in 

 spite of their complexity, point to these islands as a field where 

 special tests of the eustatic hypothesis should be made. 



Atlantic Coastal Plain of the United States. — Other questions arise 

 in connexion with the lower parts of Atlantic coastal plains recently 

 emerged. For example, the Cape May formation of New Jersey 

 and Pennsylvania and the correlated Talbot formation of Maryland 

 emerged from the sea not many thousand years ago. Their surfaces 

 lie in general below the 20 ft. contour, but strata with surfaces 

 at 40 or 45 feet have been included in each formation. In the north 



1 W. B. Wright, The Quaternary Ice Age, London, 1914, p. 423 ; The 

 Geology of the British Isles, edited by J- W. Evans {Handbuch der regionalen 

 Geologie, iii. 1), The Hague, 1918, p. 299. Cf. J. Prestwich, Quart. Journ. Geo). 

 Soc, vol. xlviii, 1892, p. 263. 



