T. S. Hunt on the Oriticisms of Prof. Dana. 49 
the origin of the various magnesian silicated rocks, hitherto 
generally regarded as the product of epigenesis, the latter has 
proposed to designate the process as diagenesis; a term which 
I adopt, as one well fitted to denote the generation of all kinds 
of erystalline rocks through a molecular re-arrangement of 
sedimentary deposits, of whatever origin. Prof. Dana, in com- 
mon with most other geologists, admits in his Manual the 
production by diagenesis of the rocks of the first class, but in 
the case of serpentine and steatite declares them to have been 
formed by epigenic pseudomorphism or chemical alteration of 
pyroxenic and other crystalline rocks; the origin of which is 
important chapters in geological treatises.” [This Journal, I, 
That Prof. Dana has receded from the extreme 
views on this subject which he maintamed from 1845 to 1858, 
and which I have constantly opposed, seems probable; but 
until he formally rejects them, the student of geology will not 
wnnaturally suppose that he still gives the sanction of 
authority to the doctrine which he once taught, without any 
qualification, but now repudiates, that “metamorphism ts pseu- 
domorphism on a broad scale.” : 
i, Dana having clearly defined the proposition that the 
chemical alterations which are recognized in individual cryst 
are to be conceived as extending to rock-masses; and having 
moreover asserted that the principle of the identity of metamor- 
phism and pseudomorphism “bears on all crystalline rocks,” is 
logically committed to all the deductions as to the changes of 
tocks which the transmutationist school has drawn from the 
“upposed alteration of minerals. By reference to the table of 
Pseudomorphs in the fourth edition of Dana’s Mineralogy, it 
will be seen that each one of the metamorphoses of rocks men- 
* ema _I shall however show, in addition, that in eac 
“te plication of the principle to rock-masses has been recog- 
nized by 
It would be easy, did space permit, to extend greatly this list of 
supposed transmutations. The various associations of rocks 
; y: ~ ¥ 
gton Smyth, in his address already quoted, “to offer a 
Premium to the ingenious for inventing an almost infinite 
Am. Jour. So1r.—Tuirp Series, Vou. IV, No. 19.—Jury, 1872, 
4 
