M2 Prof. J. Joly on the 



its present area. In his Traite de Gdoloyie, De Lapparent, in 

 a series of well-known restorations o£ ancient geography, 

 shows how far, as judged by the sediments, there was 

 transgression of the sea upon the land at various epochs. 

 It does not appear that we can infer, even at the climax of 

 the great Cenomanian transgression, that the existing land 

 was at any time covered to one half its extent. And 

 mindful of the fact that the area of denudation is in most 

 cases much greater than that of deposition, when the latter 

 is greatest the necessity of accounting for the former 

 involves the assumption that tracts of land now submerged 

 were then exposed. Without assuming the former existence 

 of lost continents in the central oceanic basins, there seems 

 very strong evidence for the disappearance of former land. 

 The evidence is found in our own Islands, in N. America, 

 in India, South Africa and Australia, and elsewhere. We 

 have to recognize continual fluctuations, but the evidence for 

 a prevailing reduction of continental areas by as much as 

 50 per cent., or even 25 per cent., in the past is, so far as I 

 know, not forthcoming. We might go further and state 

 that so great a diminution of existing land area as 50 per cent, 

 certainly did not prevail in the past. Such a redaction involves 

 about 25 per cent, of the present rate of solvent denudation, 

 and increases the age accordingly. 



Meteorological conditions, unless occasioned by a prevailing 

 change in the amount of solar heat, cannot be supposed to 

 have steadily affected in one direction the rate of denudation. 

 It is worthy of note, that the testimony derived from the 

 solvent denudation of the continents shows that climatal 

 conditions do not, within the limits, seriously affect the 

 rate of solvent denudation. This finds explanation in the 

 extremely complex nature of the factors concerned in rock- 

 weathering and rock-solution. Now the mere abundance of 

 life throughout the world in every age since the Cambrian, 

 and very certainly in pre-Cambrian times also, is sufficient 

 indication that climatal conditions cannot have been so extreme 

 as to seriously inhibit denudation. It would be easy to cite 

 evidence from sun-cracked sediments dating back to Torri- 

 donian times, from teeming oceanic life now confined to tepid 

 seas, but at various periods of geological history inhabiting 

 every part of the ocean, and finally from forest growth and 

 insect life on the land, that there is no evidence for continued 

 lessened solar heat in past ages. 



But existing soil-conditions might be exceptional. There 

 aie to-day great sheets of glacial clays -spread over the 



