1875.] 109 [Hunt. 



notice of my lately published volume of " Chemical and Geological 

 Essays," in which I have reprinted, with some additions (pages 317- 

 322) from the same Journal fjr July, 1872, my reply to his earlier 

 attack upon me, called out by my Presidential address before the 

 American Association for the Advancement of Science in August, 

 1871 (ibid,, pages 283-312). Under these circumstances I deem it 

 due alike to myself and to the cause of truth, to make a brief reply 

 to his repeated assaults. As I have, in the pages just cited, discussed 

 at some length the views of Naumann and of Delesse, to whom Dana 

 refers, I now simply call attention to the fact that I have there shown 

 that the views of the latter in the course of his studies in metamor- 

 phism and pseudomorphism underwent a complete change, as shown 

 by his successive publications in 1858, 1859 and 1861. He at first 

 taught the epigenic derivation of serpentine, steatite and chlorite from 

 granite and trappean rocks, a notion which he abandoned in 18£1 tor 

 that previously taught by myself, according to which these magnesian 

 rocks have originated from the diagenesis of sedimentary hydrous 

 magnesian silicates of aqueous formation. 



For in my years past my studies have been directed to the origin 

 of mineral species, a question hardly less important for geology than 

 is the origin of species of plants and animals for botany and zoology 

 and the views which I have arrived at, though treated as worthless 

 by Prof. Dana, seem to have met with approval and acceptance from 

 Delesse, Credner, Gumbel and Favre (ibid., pages 297, 317, 304, 

 305, 347, 348), 



In discussing in 1871, in the above mentioned address, the ques. 

 tions which arise in this connection, I took occasion to notice the very 

 generally received hypothesis of derivation by epigenesis or pseudo- 

 morphism, which, as interpreted by its various expounders, admits of 

 many remarkable transformations of one mineral species into another, 

 and to point out some objections to this view. In this discussion I 

 mentioned Prof. Dana's name in connection with some seven or eight 

 others, as having taught the doctrine of pseudomorphism by altera- 

 tion, and then proceeded to give numerous examples of the supposed 

 change of one crystalline rock into another, as maintained by various 

 authors of this school. I, moreover, stated that Prof. Dana had, in 

 1858, resumed his own teachings on this subject by declaring that 

 " metamorphism is pseudomorphism on a grand (broad) scale." 



To these statements Prof. Dana replied in 1872, that a part of the 

 supposed rock-transformations mentioned by me had never been con- 



