Level-of-no-Strain in a Cooling Globe. 215 



Islands, themselves folded ; a most remarkable fact, for which 

 we are indebted to Dr. Ghrppy's intrepidity and love of 

 science. Assuming the correctness of all the facts made 

 known by Dr. Guppy, they appear to me inconsistent with 

 the assumption that the deposits took place on submerged 

 volcanic peaks, for it is difficult to see how folding could 

 originate in such a position by any cause now known. But 

 in any case it points to an elevation of the sea-bottom, esti- 

 mated by Dr. Guppy at 12,000 feet*. 



In reading the accounts of various observers scattered over 

 the face of the globe, nothing has struck me more than the 

 universality of the evidences — side by side — of recent depres- 

 sion and recent elevation in each and every country. It 

 would be wearisome to recount them here. We know that 

 the great continental masses are built up of sedimentary rock- 

 systems, some of them reaching, in the locus of mountain- 

 ranges, an estimated thickness of ten miles. Now let us see 

 what this means. It indicates that the crust of the earth on 

 these areas has been bent to a depth double that of the deepest 

 of the deep-sea soundings. 



Yet these very deposits now constitute the highest moun- 

 tain-ranges ! With these evidences of flux and reflux before 

 our eyes, it seems really useless to invoke as an explanation 

 the aid of a secular change tending to act more or less con- 

 stantly in one direction. The investigation of the properties 

 of a cooling globe and the discovery of the existence of a level- 

 of-no-strain only a few miles beneath our feet, have greatly 

 helped to clear the ground for the reception of a theory of 

 mountain-formation which takes more fully into account the 

 actualities of nature. 



It may, however, be desirable, in the light of these recent 

 discoveries, to try and trace by geological or other observations 

 whether any features of the earth are directly attributable to 

 secular cooling. Such would be a difficult inquiry, superim- 

 posed as I believe the effects will be found to be (if found at 

 all), upon much more pronounced features due to other 

 agencies. 



Here for the present I must leave the subject, perhaps to 

 return to it at a future time. 



* ' Geology of the Solomon Islands ' (1887). " Observations on the 

 recent Calcareous Formations of the Solomon Group made during 

 1882-4 by H. B. Guppy, M.B., F.G.S.," Trans. Boy. Soc. of Edin. 1885, 

 p. 545. 



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