(B.) Reply by Dr. Hunt to Chemical Objections—(Ibid.).
"In the Proceedings of the Royal Irish Academy, for July 12, 1869, Messrs. King and Rowney have given us at length their latest corrected views on various questions connected with Eozoon Canadense. Leaving to my friend, Dr. Dawson, the discussion of the zoological aspects of the question, I cannot forbear making a few criticisms on the chemical and mineralogical views of the authors. The problem which they had before them was to explain the occurrence of certain forms which, to skilled observers, like Carpenter, Dawson, and Rupert Jones, appear to possess all the structural character of the calcareous skeleton of a foraminiferal organism, and moreover to show how it happens that these forms of crystalline carbonate of lime are associated with serpentine in such a way as to lead these observers to conclude that this hydrous silicate of magnesia filled and enveloped the calcareous skeleton, replacing the perishable sarcode. The hypothesis now put forward by Messrs. King and Rowney to explain the appearances in question, is, that all this curiously arranged serpentine, which appears to be a cast of the interior of a complex foraminiferal organism, has been shaped or sculptured out of plates, prisms, and other solids of serpentine, by “the erosion and incomplete waste of the latter, the definite shapes being residual portions of the solid that have not completely disappeared.” The calcite which limits these definite shapes, or, in other words, what is regarded as the calcareous skeleton of Eozoon, is a ‘replacement pseudomorph’ of calcite taking the place of the wasted and eroded serpentine. It was not a calcareous fossil, filled and surrounded by the serpentine, but was formed in the midst of the serpentine itself, by a mysterious agency which dissolved away this mineral to form a mould, in which the calcite was cast. This marvellous process can only be paralleled by the operations of that plastic force in virtue of which sea-shells were supposed by some old naturalists to be generated in the midst of rocky strata. Such equivocally formed fossils, whether oysters or Foraminifers, may well be termed pseudomorphs, but we are at a loss to see with what propriety the authors of this singular hypothesis invoke the doctrines of mineral pseudomorphism, as taught by Rose, Blum, Bischof, and Dana. In replacement pseudomorphs, as understood by these authors, a mineral species disappears and is replaced by another which retains the external form of the first. Could it be shown that the calcite of the cell-wall of Eozoon was once serpentine, this portion of carbonate of lime would be a replacement pseudomorph after serpentine; but why the portions of this mineral, which on the hypothesis of Messrs. King and Rowney have been thus replaced, should assume the forms of a foraminiferal skeleton, is precisely what our authors fail to show, and, as all must see, is the gist of the whole matter.
"Messrs. King and Rowney, it will be observed, assume the existence of calcite as a replacement pseudomorph after serpentine, but give no evidence of the possibility of such pseudomorphs. Both Rose and Bischof regard serpentine itself as in all cases, of pseudomorphous origin, and as the last result of the changes of a number of mineral species, but give us no example of the pseudomorphous alteration of serpentine itself. It is, according to Bischof, the very insolubility and unalterability of serpentine which cause it to appear as the final result of the change of so many mineral species. Delesse, moreover, in his carefully prepared table of pseudomorphous minerals, in which he has resumed the results of his own and all preceding observers, does not admit the pseudomorphic replacement of serpentine by calcite, nor indeed by any other species.[AV] If, then, such pseudomorphs exist, it appears to be a fact hitherto unobserved, and our authors should at least have given us some evidence of this remarkable case of pseudomorphism by which they seek to support their singular hypothesis.
[AV] Annales des Mines, 5, xvi., 317.
"I hasten to say, however, that I reject with Scheerer, Delesse and Naumann, a great part of the supposed cases of mineral pseudomorphism, and do not even admit the pseudomorphous origin of serpentine itself, but believe that this, with many other related silicates, has been formed by direct chemical precipitation. This view, which our authors do me the honour to criticise, was set forth by me in 1860 and 1861,[AW] and will be found noticed more in detail in the Geological Report of Canada, for 1866, p. 229. I have there and elsewhere maintained that ‘steatite, serpentine, pyroxene, hornblende, and in many cases garnet, epidote, and other silicated minerals, are formed by a crystallization and molecular re-arrangement of silicates, generated by chemical processes in waters at the earth’s surface.’[AX]
[AW] Amer. Journ. Science (2), xxix., 284; xxxii., 286.
[AX] Ibid., xxxvii., 266; xxxviii., 183.
"This view, which at once explains the origin of all these bedded rocks, and the fact that their constituent mineral species, like silica and carbonate of lime, replace the perishable matter of organic forms, is designated by Messrs. King and Rowney ‘as so completely destitute of the characters of a scientific hypothesis as to be wholly unworthy of consideration,’ and they speak of my attempt to maintain this hypothesis as ‘a total collapse.’ How far this statement is from the truth my readers shall judge. My views as to the origin of serpentine and other silicated minerals were set forth by me as above in 1860-1864, before anything was known of the mineralogy of Eozoon, and were forced upon me by my studies of the older crystalline schists of North America. Naumann had already pointed out the necessity of some such hypothesis when he protested against the extravagances of the pseudomorphist school, and maintained that the beds of various silicates found in the crystalline schists are original deposits, and not formed by an epigenic process (Geognosie, ii., 65, 154, and Bull. Soc. Geol. de France, 2, xviii., 678). This conclusion of Naumann’s I have attempted to explain and support by numerous facts and observations, which have led me to the hypothesis in question. Gümbel, who accepts Naumann’s view, sustains my hypothesis of the origin of these rocks in a most emphatic manner,[AY] and Credner, in discussing the genesis of the Eozoic rocks, has most ably defended it.[AZ] So much for my theoretical views so contemptuously denounced by Messrs. King and Rowney, which are nevertheless unhesitatingly adopted by the two geologists of the time who have made the most special studies of the rocks in question,—Gümbel in Germany, and Credner in North America.