NOTES TO BOOK XVIII. 689 



remains in strata, has received other very striking acces- 

 sions by the labours of Prof. Edward Forbes in observing 

 the marine animals of the JEgean Sea. He found that 

 even in their living state, the mollusks and zoophytes are 

 already distributed into strata. Dividing the depth into 

 eight regions, from 2 to 230 fathoms, he found that each 

 region had its peculiar inhabitants, which disappeared 

 speedily either in ascending or in descending. The zero of 

 animal life appeared to occur at about 300 fathoms. This 

 curious result bears in various ways upon geology. Mr. 

 Forbes himself has given an example of the mode in which 

 it may be applied, by determining the depth at which the 

 submarine eruption took place which produced the volcanic 

 isle of Neokaimeni in 1707- By an examination of the 

 fossils embedded in the pumice, he showed that it came from 

 the fourth region. (British Assoc. Reports, 1843, p. 177-) 



To the modes in which organized beings operate in 

 producing the materials of the earth, we must add those 

 pointed out by the extraordinary microscopic discoveries of 

 Professor Ehrenberg. It appears that whole beds of earthy 

 matter consist of the cases of certain infusoria, the remains 

 of these creatures being accumulated in numbers which it 

 confounds our thoughts to contemplate. 



(GA.) p. 614. The theory of craters of elevation pro- 

 bably errs rather by making the elevation of a point into 

 a particular class of volcanic agency, than by giving vol- 

 canic agency too great a power of elevation. 



I have modified the expressions used in the text with 

 regard to those writers who have applied mathematical 

 reasoning to geological questions. Such reasoning, when 

 it is carried to the extent which requires symbolical pro- 

 cesses, has always been, I conceive, a source, not of know- 

 VOL. III. Y Y 



