494 ADDRESS OF T. STERRY HUNT. 
point from a plutonic basis.” 
I then asserted that the problem to be solved in regional meta- 
morphism is the conversion of sedimentary strata, ‘derived by 
chemical and mechanical agencies from the ocean-waters and pre- 
existing crystalline rocks into aggregations of crystalline silicates, 
These metamorphic rocks, once formed, are liable to alteration 
only by local and superficial agencies, and are not, like the tissues 
of a living organism, subject to incessant transformations, the 
pseudomorphism of Bischof.” * 
I had not, at that time, seen the essay by ,Delesse on Pseudo- 
morphs already referred to, published in 1859, in which he mam- 
tained views similar to those set forth by me in 1853 and 1860, 
declaring that much of what had been regarded as pseudomor- 
phism had no other basis than the observed associations of miner- 
als, and that often ‘‘ the so-called metamorphism finds its natural 
explanation in envelopment.” These views he ably and ingeni- 
ously defended by a careful discussion of the whole range of facts 
belonging to the history of the subject. 
My own expression of opinion on this question, in 1853, had 
been privately criticised, and I had been charged with a want of 
comprehension of the question. It was, therefore, with no small 
pleasure, that I not only saw my views so ably supported by 
Delesse, but read the language of Carl Friedrich Naumann, who 
in 1861 wrote to Delesse as follows, referring to his essay just 
_noticed :— 
“You have rendered a veritable service to science in restricting 
pseudomorphs to their true limits, and separating what had been 
erroneously united to them. As you have remarked, envelop- 
ments have, for the most part, nothing in common with pseu 
orphs, and it is inconceivable that they have been united by 50 
that they commit an analogous error, w they regard gneisses, 
amphibolites, etc., as being, all of them, the results of amor- 
phic epigenesis, and not original rocks. It is precisel use 
i y becat 
pseudomorphism has been so often confounded with metamorphisti 
that this error has found acceptance. I only admit a pseudomorp 
e 
* Amer. Jour. Sci., II, xxx, 135. 
