§2 On the Advancement of Geological Science in India. [Jan. 



in his valuable work of 1S3G, shews that the chemical composition is 

 the best basis on which to classify minerals, and he gives the component 

 parts of nearly 500, many of which were analysed in his own labora- 

 tory. In the elementary state of our knowledge on this subject, it is 

 not to be wondered at, that many discrepancies occur. Klaproth gives 

 an analysis of hornblende, by which he makes it ferruginous, containing 

 thirty-three per cent of iron, and only three of magnesia, but Dr. 

 Thomson's hornblende is magnesian, containing thirteen per cent of 

 magnesia. There is little doubt, but that the two specimens must dif- 

 fer much in appearance, and we may therefore avoid the xiistakes, 

 which would be produced by preserving typical specimens of the mi- 

 nerals to which we apply a name. 



Mineralogy considers only single minerals, and compound rocks com- 

 posed of these minerals are therefore excluded from the science. This 

 subject, a sort of " rockology," might be considered a science of itself, 

 tut we are destitute, almost entirely, of any information on the subject. 

 Dr. MaccuUoch is the only one who has given it sufficient attention. His 

 work " On Rocks" of 1821, however, has many objections, and although 

 very useful, a fresh work is very much wanted. The nomenclature 

 also requires complete revision to prevent the absurd contradictions 

 that writers have fallen into. We find eiirite defined by the best autho- 

 rities as " felsphatic granite containing crystals of felspar," — " a gra- 

 nite composed principally of felspar, finely granular or nearly compact," 

 ■ — composed principally of compact felspar" — as being another terra 

 for " compact felspar." Chert is called ** hornstone" — indurated 

 lime stone"—** a modification of silicious earth" — *' Paris burr stone" — 

 ** a cavernous silicious rock." Hornstone is, "flinty slate without the 

 slaty fracture" — "silicious schist" — "strongly resembles basalt." — Dial- 

 lage rock is "diallage and saussurite" "diallage and felspar." Saussurite 

 is " hard silicious serpentine" — " jade or anestone" — ** nephite," and so 

 forth : the names being applied at the fancy of the observer, uniil they 

 may be shewn to mean literally nothing. The multiplication oi names 

 I consider to have caused the greatest injury to the science, and I con- 

 ceive them to be by no means necessary, for by combining the generic 

 term for a mineral, with other terms, denoting the structure &g., I think 

 we may in great measure avoid their use without being misunderstood. 

 As an example we may take a single mineral " hornblende ;" then we 

 have ^^crystalline hornblende," or aggregated in large crystals; ''granular 

 hornblende ;" " compact hornblende" (if such a rock be found); gra^ 

 «z72c hornblende."— Hornblende rock or black granite,— " hornblende 

 porphyry." — Hornblende in grains embedded in a paste of felspar, the 

 porphyritic sienite of Jameson, " schistous hornblende porphj ry." — 



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