Gregory — Progress in Interpretation of Land Forms. 119 



as "irresistible proof of paroxysmal action," and Hop- 

 kins (1852), who contended for "currents produced by 

 repeated elevatory movements." 



After his arrival in America (1846), Agassiz's influ- 

 ence was felt, and his paper on the erratic phenomena 

 about Lake Superior (1850), 43 in which he called upon 

 the advocates of water-borne ice to point out the barrier 

 which caused the current to subside, produced a salu- 

 tary effect; yet Desor (1852) 4,i states that in the region 

 described by Agassiz "the assumption [of a general ice 

 cap] is no longer admissible," and that the bowlders on 

 Long Island "were transported on ice rafts along the sea 

 shore and stranded on the ridges and eminences which 

 were then shoals along the coast." Twenty years of 

 discussion were insufficient to establish the glacial theory 

 either in Europe or America. The consensus of opinion 

 among the more advanced thinkers in 1860 is expressed 

 by Dana : 47 



"In view of the whole subject, it appears reasonable to con- 

 clude that the Glacier theory affords the best and fullest 

 explanation of the phenomena over the general surface of the 

 continents, and encounters the fewest difficulties. But icebergs 

 have aided beyond doubt in producing the results along the 

 borders of the continents, across ocean-channels like the German 

 Ocean and the Baltic, and possibly over great lakes like those of 

 North America. Long Island Sound is so narrow that a glacier 

 may have stretched across it." 



Papers in the Journal of 1860-70 show 7 a prevailing 

 belief in icebergs, but the evidence for land ice was 

 accumulating as the deposits became better known, and 

 in 1871 field workers speak in unmistakable tones : 4S 



* ' It is still a mooted question in American geology whether the 

 events of the Glacial era were due to glaciers or icebergs. . . . 

 American geologists are still divided in opinion, and some of the 

 most eminent have pronounced in favor of icebergs. 



Since, then, icebergs cannot pick up masses tons in weight 

 from the bottom of a sea, or give a general movement southward 

 to the loose 'material of the surface; neither can produce the 

 abrasion observed over the rocks under its various conditions; 

 and inasmuch as all direct evidence of the submergence of the 

 land required for an iceberg sea over New England fails, the 

 conclusion appears inevitable that icebergs had nothing to do 

 with the drift of the New Haven region, in the Connecticut 

 valley; and, therefore, that the Glacial era in central New Eng- 

 land was a Glacier era." 



