A NATURAL SYSTEM IN MINERALOGY. wir 
the crystalline rearrangement of previously-formed detrital silicates, and the production 
of new ones, by “the chemical union of heterogeneous elements” present in the sedi- 
ments—processes in either case resulting in the “local development of crystalline sili- 
cates in the texture of clastic rocks.” By all of these methods, crystalline species such as 
quartz, hematite, amphibole, feldspars, garnet, epidote and various micas, as well as ser- 
pentine, glauconite and sepiolite, appear occasionally in sedimentary strata, alike of palæo- 
zoic and'of more recent times. The occurrence of these, and of other species, under such 
conditions has helped to sustain the arguments of those who imagine a very different 
action from these, resulting in the complete transformation of ordinary detrital rocks, such 
as sands and clays, by some metasomatic process, into typical granites, gneisses, and horn- 
blendic and micaceous schists. Of this doctrine of unexplained and inexplicable trans- 
mutations, through which isolated portions of earthy sediments of later periods are sup- 
posed to have been changed into various types of crystalline schists, which in certain areas 
are indistinguishable from those of earlier eozoic times, it need only be said that the 
SuB-ORDER III. — PERSILICATE, 







ei 11. Perzrourtorp.| 12. PERSPATHOID. 13. PHRADAMANTOIN. 14. PerpyLLoin. | 15. ARGILLOID. 
ee lege V= 1717-2 V= 5-744 V=61-51 V =65—5-4 
TUE eee Eee TS, d'encre Ale pap Se een en gen = lee - ee - - Schrütterite. 
1:K# |-------|-----.- - | Dumortierite. - - - - - - - - - - - - - 7 | Collyrite. 
U:K% |------+-/------ | pes aaa cere eee Pie ete 7e Allophane. 
1:2 | Westanite.- - - |{Pyniytite.  } |{PEnoante Viveone Malacone, À || Halcosti (5 : 6). || Samoite 
HR I) aio Ss Sees Stone eo Ole poke iS ioe = - Kaolinite. - - - - | Kaolin. Halloysite, 
1:1% REC 2e = - - - - - - | Auerbachite. - - - - - - - - Hisingerite. 
ED TOO EE Were ES à BNR PETS STATE Pyrophyllite. - - - |p erate ondatte. 
AS de | TEE aimes bio Pyrophyllite. - - - RE 
5 PIE METTENT ORNE MERE Anthosiderite. - - - - - - - DAMON ER Cimolite. 
L 1:4 MÉTIERS EN = leh= tele === = poe ooh aa Smectite. 


supposed examples of it have, one by one, been disproved and abandoned by their former 
advocates. The whole doctrine of regional metamorphism, as maintained by Huttonians, 
was an attempt to substitute the intervention of miracles for the established order of 
mineralogical development.’ 
§ 17. In discussing, in the essay on a Natural System in Mineralogy, the question of 
the chemical constitution and the different degrees of condensation in mineral species, in 
connection with the doctrines of high equivalent weights and polymerism, which are there 
maintained, we have, in deference to the general usage of chemists, employed the terms 
“molecular weight” and “ molecular volume,” although they are in contradiction to our 
own conceptions of the philosophy of chemistry. Moreover, while therein asserting that 
liquids and solids are polymers of gaseous species, and their equivalent weights conse- 
quently multiples of the unit-weights deduced from chemical analysis and vapor-density, 
we have said the. “ molecular weights of these are as yet unknown,” and moreover, 


! The succeeding portions of this paper were not communicated till August, 1886. 
