50 T. S. Hunt on the Criticisms of Prof. Dana. 
series of possible combinations and permutations.” Before pro- 
ceeding 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 product as direct sub- 
stitution. 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 
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 substi- 
tution.” [Dana’s Mineralogy, 5th edition, 361.] Since quartz, 
orthoclase and albite can be replaced by calcite, the transmuta- 
tion of granite or gneiss into limestone presents no difficulty. 
I cannot, at present, give the reference to the statement of 
Volger that some gneissoid limestones owe their origin to such 
a process. 
Metamorphosis of limestone to dolomite. This change 1s 
maintained by von Buch, Haidinger and many others. I am 
blamed for mentioning in connection with this-school the name 
of Haidinger, who, Prof. Dana says, “never wrote upon the 
subject of the alteration of rocks.” It has, however, never 
before been questioned that Haidinger was the first, if not to 
suggest, to clearly set forth the theory of the supposed conver- 
sion of limestone into dolomite by the action of magnesian solu- 
tions, aided by heat and pressure; a theory which I have else- 
where refuted. [Bischof, Chem. Geology, iii, 155, 158; Zirkel, 
Petrographie, i, 246 ; Liebig and Kopp, Jahresbericht, 1847-48, 
1289, and this Journal, I, xxvii, 376]. 
Metamorphosis of dolomite to serpentine. This change is 
maintained by G. Rose [Bischof, Chem. Geol., ii, 423], and by 
Dana [this Journal, III, iii, 89]. 
Metamorphosis of granite, granulite, and eclogite directly into 
serpentine, chlorite and tale. These transmutations are main- 
tained by Miiller, and adopted by Bischof. [Chem. Geol., ii, 
424, 434. | 
trine from the pages of Bischof’s work already quoted. Meta- 
morphosis of diorite, hornblende-rock and labradorite to serpen- 
tine; G. Rose, Breithaupt, von Rath [ii, 417,418]. Diorite and 
