216 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jail. 10, 



XI. Conclusion. 



Prom what has been stated in some of the preceding pages, 

 respecting the varions chemical changes which " eozoonal " Ophite 

 appears to have undergone, and its mineralogical constituents, we 

 are strongly inclined to believe that it is a pseudoraorphic rock, that 

 it existed at one time in the ordinary metamorphic state, perhaps as 

 hornblendic or augitic gneiss, and that it is primarily of sedimentary 

 origin*. "Whether the same may be concluded of all ophitic rocks is 

 a question on which we cannot offer any opinion — negative, or affir- 

 mative. There are some grounds for believing, however, that certain 

 dolerites, generally considered to be of eruptive origin, have become 

 changed into Ophite: and though we have not detected any " eozoonal" 

 structure in an example apparently of the kind, from Monzoni in the 

 Tyrol, which has fallen under our observation, it would not surprise 

 us if this structure were found in ophitic rocks supposed to belong 

 to the eruptive section, considering that the essential mineral (augite) 

 of dolerite contains a large percentage of silicate of limef . 



* Dr. Sterry Hunt states that "pseudomorphism, which is the change of one 

 mineral species into another by the introduction or the elimination of some ele- 

 ment or elements, presupposes metamorphism, since only definite mineral species 

 can be subject to this process " (see Journal of the Geological Soc. of Dublin, vol. 

 X. p. 88). We accept this view of pseudomorphism ; but we see no reason why 

 the change can only have " taken place in some mineral species, in reins, and 

 near the surface" — why it cannot have operated on a suificiently extensive scale 

 to generate the layers and beds of Ophite interstratified with the Laurentian 

 limestones and gneiss of Canada. It may be, that " the alteration of great masses 

 of silicated rocks by such a process is as yet an improved hypothesis :" we 

 cannot but think, however, that Dr. Hunt has insufficiently estimated the evidence 

 which may be adduced in its favour. One which we shall now cite seems to 

 bear us out in this idea: alluding to Blum's discovery of pseudomorphs of ser- 

 pentine after augite, at Monzoni, Bischof expressly states, " it is not merely the 

 fine crystals, which occur in its drusy cavities and fissures, that are changed, but 

 the whole mass of the rock is converted into serpentine" (See Chem. and Phys. 

 Geology, vol. ii. p. 322). 



t Sir Charles Lyell has stated that " even if we had not discovered the Eozoon, 

 we might fairly have inferred" that the " calcareous masses, from 400 to 1000 

 feet and more in thickness," associated with it "were originally of organic 

 origin" (Elements of Geology, 6th edition, p. 580). Now, whatever the "cal- 

 careous masses " may have originated from, the idea of their being " eozoonal " 

 must be abandoned. We do not dispute the above inference, which, be it con- 

 sidered, does not necessarily involve animal agency alone, as such " masses " 

 may be the debris of calciphytes, like the calcareous accumulations still abun- 

 dant on many of our present sea-bottoms and resulting from the growth and 

 decay of various kinds of nullipores. But it may turn out that they are not of 

 organic origin at all. Doubtless some, calling to mind the beds of travertine oc- 

 curring at Kome, may be disposed to regard them as of chemical origin. Another 

 idea, however, strikes us just now. Feeling confident in the view herein taken 

 of the origin of " eozoonal" Ophite, we are strongly inclined to believe that its 

 calcareous portions are segregations derived partly, or wholly, from the silicate 

 of lime contained in hornblendic or augitic rocks, such silicate having been con- 

 verted into a carbonate by the introduction of water containing free or combined 

 carbonic acid. (In lime-magnesia augite, as diopside, these bases, important in 

 " eozoonal" Ophite, amount to about 43 per cent.) There are some grounds for 

 believing that the lenticular masses of saccharoidal calcite, or " primary " marble, 

 often imbedded in metamorphic rocks, have originated in the same way. But 

 whether the vast " calcareous masses," referred to by Lyell, are of pseudomorphic 

 origin is a question on which it behoves iis to speak with less confidence ; at any 

 rate, such a view, as will now be seen, ought to command due consideration. 



