Elevation and Subsidence of the Surface of the Earth. 413 



pressure could not have been the sole agent in the operation ; for 

 the cleavage did not take place on the first upheaval of the dis- 

 trictj when, the crust not having yet given way, the pressure 

 might be supposed the greatest, but only after the beds had 

 assumed their present position and the various anticlinal axes 

 had been formed/^ The Herschel-Babbage theory, however, 

 entirely gets over this difficulty ; for the pressure would not be 

 so great during the upheaval caused by limestone, as afterwards 

 when the refrigeration and contraction consequent on denudation 

 had come into play ; for the extra weight thus thrown on to the 

 underlying superheated rocks would give rise to an upward 

 pressure which would force dykes into the overlying beds, and 

 give rise to a cleavage that would either obliterate former ones, 

 or intensify them where the planes of the two coincided. 



Conclusion. — If the surface of the earth were level and the sea 

 spread evenly over it, the depth of this universal ocean would be 

 at least two miles ; and as we cannot suppose that in a sphere 

 slowly cooling from an incandescent state any gases or other vo- 

 latile substances would have been retained in the interior so as 

 to produce eructations on the surface, the question naturally 

 arises, what could first have caused the subversion of the equili- 

 brium that has ultimately led to such stupendous changes? 

 There can only, I think, be one answer to this question, viz. the 

 origin of life on the globe. This life, by abstracting the carbo- 

 nate of lime from solution in the sea* and depositing it on the 

 bottom first disturbed the equilibrium, and prepared the way 

 for the countless multitude of forms that now crowd over the 

 surface of the globef. When the earth was entirely enveloped 

 by the ocean, the trade- winds would cause surface-currents flow- 

 ing in N.E. and S.E., and undercurrents flowing in N.W. and 

 S.W. directions; and if we suppose life to have originated at 

 any one spot these currents would spread the organisms in these 

 directions, and the first deposits, and consequently the strike of 

 the first-elevated rocks, would have these directions also. The 

 direction of the first land, by aff'ecting the distribution of 

 future deposits, would probably exert an influence even up to 



* Bischof (Chemical Geology, vol. iii. p. 37) and Sterry Hunt (American 

 Journal of Science [2J vol. xxxix. p. 184) both agree that the })rimeval 

 ocean probably contained carbonate of hme in solution. 



t It follows from this that it is to the ocean that we must look for the 

 nearest representatives of primordial life. The freshwater monads and 

 bacteria are probably quite complicated beings compared with the first- 

 formed organisms. It may be that the organic matter distributed through 

 the ocean at great depths, and which is so small as to be invisible to our 

 most powerful microscopes, and only capable of being recognized by che- 

 mical reagents, is (composed of living organisms intermediate in structure 

 between the Rhizopoda and the first living germs. 



