1844—185 8 ] ELEVATION AND SUBSIDENCE 91 



But would not this be a measure of the movement in Letter 47 

 ever) - other area, northern (arctic), antarctic, or tropical, 

 during an equal period— oceanic or continental? For the 

 conversion of sea into land would always equal the turning 

 of much land into sea. 



But all this would be done in a fraction of the Pliocene 

 period ; the Glacial shells are barely 1 per cent, extinct 

 species. Multiply this by the older Pliocene and Miocene 

 epochs. 



You also forget an author who, by means of atolls, con- 

 trived to submerge archipelagoes(orcontinentsP), the mountains 

 of which must originally have differed from each other in 

 height 8,000 (or 10,000 ?) feet, so that they all just rose to the 

 surface at one level, or their sites are marked by buoys of 

 coral. I could never feel sure whether he meant this 

 tremendous catastrophe, all brought about by what Sedgwick 

 called " Lyell's niggling operations," to have been effected 

 during the era of existing species of corals. Perhaps you 

 can tell me, for I am really curious to know. 1 . . . 



Now, although there is nothing in my works to warrant the 

 building up of continents in the Atlantic and Pacific even 

 since the Eocene period, yet, as some of the rocks in the 

 central Alps are in part Eocene, I begin to think that all 

 continents and oceans may be chiefly, if not all, post-Eocene, 

 and Dana's " Atlantic Ocean " of the Lower Silurian is 

 childish (see the Anniversary Address, 1856). 2 But how far 

 you are at liberty to call up continents from " the vasty 

 deep " as often as you want to convey a Helix from the 

 United States to Europe in Miocene or Pliocene periods is 

 a question ; for the ocean is getting deeper of late, and 

 Haughton says the mean depth is eleven miles ! by his late 

 paper on tides. 3 I shall be surprised if this turns out true by 

 soundings. 



I thought your mind was expanding so much in regard 

 to time that you would have been going ahead in regard to 

 the possibility of mountain-chains being created in a fraction 



1 The author referred to is of course Darwin. 



2 Probably Dana's Anniversary Address to the American Association 

 for the Advancement of Science, published in the Proceedings 1856. 



3 " On the Depth of the Sea deducible from Tidal Observations " 

 (Proc. Irish Acad., Vol. VI., p. 354, 1S53-54). 



