A. Tylor — Formation of Deltas. 497 



regards inequalities of sea-bottom, if tlie Great Bank of Newfound- 

 land were in coral regions, and were elevated from its present 

 relative level, so that its broad platform with its common depth of 

 40 to 50 fathoms were raised about 20 fathoms, by which coral reefs 

 making germs could fix and develope themselves under fitting condi- 

 tions, we should have an area of between 35,000 to 40,000 square 

 miles, around the irregular margin of which there would be condi- 

 tions for an extended border of coral reefs : the sea round the margin 

 would often be suddenly deep. Soundings up to 149 fathoms are 

 found close to the south-eastern side of the bank." 



Supposing that the sea-bottom in the Pacific was originally of 

 similar heights to Sir H. T. De la Beche's case of the Newfoundland 

 Banks, then applying our hypothesis of the fall of 600 feet in the 

 sea-level during the Glacial Period, supposing that period to have 

 continued 138,000 years, we should have a sufficient period and also 

 a gradual change of conditions and level of sea so as to be most 

 favourable to the growth of coral banks. 



As far as the limit of 600 feet — which is a greater depth than we 

 are certain coral ever reaches below the surface of the sea — the 

 theory of a fall in the sea-level appears to explain the difficulties of 

 the subject, as well as that of gradual subsidence and elevation. 

 Having now hastily reviewed some of the more important littoral 

 deposits that might have been formed in the last 138,000 (?) years, and 

 having found that there are no greater difficulties presented by the 

 hypothesis of a change in the sea- level than occurs with the theory 

 of subsidence of the sea-bottom, I will add a few remarks on the 

 growing importance of the Glacial Period geographically considered. 



"With regard to the importance of the Glacial Period, Prof. Agassiz 

 long since wrote : — " The British Islands, Sweden, Norway and 

 Eussia, Germany and France, the mountainous regions of the Tyrol 

 and Switzerland, down to the happy fields of Italy, together with the 

 Continent of Northern Asia, formed undoubtedly but one ice-field, 

 whose southern limits investigation has not yet determined. The 

 polar, ice, which at the present day covers the miserable regions of 

 Spitzbergen, Greenland, and Siberia, extended far into the temperate 

 zones of both hemispheres, leaving probably but a broader or nar- 

 rower belt around the equator, upon which there were constantly 

 developed aqueous vapours which again condensed at the poles." 



Time has not modified Agassiz's views of the importance of ice 

 action, for he writes, p. 424, Journey in Brazil, 1868, after applying 

 the theory of ice action to the formation of immense beds of drift in 

 the valley of the Amazon, near the Equator, and the level of the sea : — 

 *' I am aware that this suggestion will appear extravagant. But 

 is it after all so improbable, that when Central Europe was covered 

 with ice thousands of feet thick — when the glaciers of Great Britain 

 ploughed into the sea, and when those of the Swiss mountains had 

 ten times their present altitude, and Northern Italy was filled with 

 ice, and these frozen masses extended into Northern Africa ; when a 

 sheet of ice reaching nearly to the summit of Mount Washington, in 

 the White Mountains (that is having a thickness of nearly 6000 



VOL. IX. — NO. CI. 32 



