324 ORIGIN OF CRYSTALLINE ROCKS. [XIII. 



fourth edition of Dana's Mineralogy, it will be seen that each one 

 of the metamorphoses of rocks mentioned in the above extract from 

 my address is based upon an asserted epigenic change or conversion 

 of the constituent species. I shall, however, show, in addition, that 

 in each case the application of the principle to rock-masses has been 

 recognized by one or more of the authorities already named, and 

 that the so-called caricature has been drawn by their own hands. 

 It would be easy, did space permit, to extend greatly this list of 

 supposed transmutations. The various associations of rocks and 

 minerals in nature, when interpreted according to the canons of this 

 school, seem, in fact, as remarked by Professor Warrington Smyth, 

 in his address already quoted, " to offer a premium to the ingenious 

 for inventing an almost infinite series of possible combinations and 

 permutations." Before proceeding further it is to be noted that no 

 distinction can, in many cases, be established between the results 

 of alteration (or partial replacement) and substitution (or complete 

 replacement) ; since successive alterations may give the same pro- 

 duct as direct substitution. Thus, for example, quartz might be 

 directly replaced by calcite, or else first altered to a silicate of lime, 

 which, in its turn, might be changed to carbonate. The alteration 

 of quartz to a silicate of magnesia, and that of both pyroxene and 

 pectolite to calcite, is maintained by the writers of the present 

 school. 



Metamorphosis of granite or gneiss to limestone : Calcite, we are 

 told, is pseudomorphous of quartz, of feldspar, of pyroxene, and of 

 garnet, besides other species ; it moreover replaces both orthoclase 

 and albite " by some process of solution and substitution." (Dana's 

 Mineralogy, 5th edition, 361.) Since quartz, orthoclase, and albite 

 can be replaced by calcite, the transmutation of granite or gneiss 

 into limestone presents no difficulty. [In the opinion of Messrs. 

 King and Rowney, the crystalline limestones of Tyree in the 

 Hebrides, those of Aker in Sweden, and similar limestones in the 

 Laurentian of North America, were at one time beds of gneiss, 

 diorite, and other silicated rocks, which have been changed by an 

 epigenic process. (Annals and Magazine of Natural History for 

 1869, Vol. XIII. page 390.) Volger has also asserted a similar 

 origin for certain gneissoid limestones.] 



Metamorphosis of limestone to dolomite : This change is main- 

 tained by Von Buch, Haidinger, and many others. I am blamed for 

 mentioning in connection with this school the name of Haidinger, 

 who, Professor Dana says, " never wrote upon the subject of the 



