VIEWS ON MINERAL SPECIES. 431 



In the system of Dana (1844) : — 



Species. Genus. Order. 



Garnet Carbunculus Hyalinea 



Felspar Spatum Chalicinea 



Scapolite Scapolus Chalicinea 



The order Gem of Mohs, with which the order 

 Chalicinea of Dana is almost identical, is defined as 

 comprising non-metallic minerals having a non-adamantine 

 lustre, and an uncoloured powder (streak), with a hardness 

 between 5^ and 10, and specific gravity between 1 '9 and 47. 



The genus Garnet of Mohs is defined as comprising 

 minerals with a lustre which is not purely vitreous, having 

 a hardness between 6 and 7, and a specific gravity between 

 3* 1 and 4*3. It includes, in addition to Garnet, the minerals 

 Idocrase, Helvine, and Staurolite. 



The genus Spatum of Dana comprises minerals having 

 a hardness between 4 and 6|-, and a specific gravity 

 between 2*1 and 2*8. It includes, in addition to Garnet, 

 the minerals Idocrase, Helvine, Staurolite, and Epidote. 



Epidote in the system of Mohs was a species referred, 

 together with Pyroxene and Amphibole, to the genus 

 Augite-spar, defined as possessing a non-metallic pearly 

 lustre, with hardness \\ to 7, and specific gravity 27 to 3*5. 



When we remember that a hardness 4^- merely signifies 

 that the mineral will scratch Fluor and is itself scratched 

 by Apatite, and that the specific gravity of garnet may vary 

 from 3 to 4, it is evident that these characters are ill suited 

 to define a species even for purposes of practical deter- 

 mination. 



THE CHEMICAL SYSTEM. 



At this period the battle was raging furiously between 

 those who supported the Natural, or as Mohs called it, the 

 Natural-historical System, and the adherents of the 

 chemical system of Berzelius. A compromise was 

 ultimately effected by the system, due largely to the in- 

 dependent labours of Rose and Rammelsberg, which 

 considers the crystalline form and the chemical composition 

 as conjointly necessary and sufficient to define a species. 

 This mode of regarding minerals is almost universally 



