531 



•wise nothing more than a pseudomorph after serpentine. # In short, we 

 see no reason to conclude otherwise than that the whole of the " eozoo- 

 nal " structures have originated through chemical substitutions. 



We have next to adduce a case, which, apart from its bearing on the 

 origin of " eozoonal" structures, is of the utmost importance in elucidat- 

 ing the phenomena manifested by pseudomorphosed minerals, and rock 

 masses. The veins, in the cases already figured, exemplify the change of 

 compact or amorphous serpentine into fibrous chrysotile, and the replace- 

 ment of the latter variety by ordinary calcite ; but in the present one 

 (Fig. 9, PI. XLIY.), the replacement has taken place unaccompanied 

 by any structural change. Before decalcification, the vein under notice, 

 which intersects some massive serpentine in one of our slabs of Conne- 

 mara ophite, seemed to be wholly filled with chrysotile; but, after be- 

 ing subjected to the action of dilute acid, we found the infilling had in 

 a great measure disappeared ; only portions of it, both compact (c) and 

 separated (d), were left adhering here and there to the walls of the 

 vacant space, now a fissure ; while at the bottom (/), where decalcifica- 

 tion had not proceeded deep enough, there still remained the infilling 

 in a completely fibrous state. But we now observed, what had not been 

 particularly noticed in our first examination, that the vein, which is 

 slightly coloured, varied in shade, the portion answering to what had 

 been dissolved out being the lightest ; it therefore became evident to us 

 that the fibrous infilling consisted of two substances, — one an insoluble 

 silicate, and the other a soluble carbonate. This case, like others that 

 have been brought forward, can only be explained by pseudomorphic 

 action — a hydro -magnesian silicate replaced by what we believe to be 



* To us this hypothesis, if even suggested to account for the formation of the irregular 

 beds of crystalline limestone interposed among the metamorphic rocks of Ireland and 

 Scotland, has more in its favour than the one promulgated by Sterry Hunt to ex- 

 plain the origin of the far greater calcareous masses belonging to the Laurentian system of 

 Canada. The existence of the latter rocks seems to have materially influenced Sir Charles 

 Lyell, Professor Ramsay, and others, in accepting the " received doctrine." A gigantic 

 foraminifer, such as " Eozoon Canadense" is reputed to have been, would have just the 

 sort of skeleton to produce reefs of limestone. But, unfortunately for this argument, 

 Sterry Hunt has most emphatically pronounced "the often-repeated assertion that 

 organic life has built up all the great limestone formations" to be " based on a fallacy :" 

 they "owe'' their " origin to chemical reactions, Avhich are still going on in the ocean's 

 waters, and which have in past times given rise directly to limestone strata ; in which 

 the occurrence of shells, corals, and Eozoon, is only accidental.'' (" Geology of Canada, 

 1866," p. 201 ; "Quarterly Journal of Geological Society," vol. xxi., p. 70). 



[In connexion with this subject, we find the following statement by Professor Hull : — 

 " The researches of Sir William Logan and his colleague of the Geological Survey of 

 Canada, followed by other naturalists, have demonstrated that even the oldest known 

 limestones on the surface of the globe owe their origin to Eozoon" ("Quarterly Journal 

 of Science," July, 1869). We much regret that this statement is open to adverse 

 criticism. It will be pronounced to be " based on a fallacy" by Dr. Sterry Hunt ; and the 

 point gratuitously assumed to be "demonstrated" by the Director of the Irish Geological 

 Survey is damagingto his ownbelief in " Eozoon ;" inasmuch as it necessitates the disprov- 

 ing of our position, that the limestones referred to (we mean the non-serpentinous) are re- 

 markable for the total absence of any reliable evidences of "eozoonal" remains. — April 

 20, 1870.] 



