62 



THOMAS STEÊEY HUNT ON A NATUEAL SYSTEM IN 



Tribe 8. — Pkotoperadamantoids. 



§ 80. We come next to the Protoperadamantoids, a very important tribe. Beginning 

 with the most highly protobasic species, we find in the first line, pargasite, which we have 

 already noticed as an aluminous amphibole, connecting the protopersilicates with the pre- 

 ceding suborder. With this we place keilhauite, a titaniferous silicate, which, like tita- 

 uite, is attacked by hydrochloric acid, a character not common to adamantoids, save 

 in the more highly basic species of the first suborder, and already noticed (§ ST). 

 In keilhauite, a part of the alumina is replaced by ferric oxyd, and in the titaniferous 

 schorlomite, Avhich is also attacked by the acid, and has a ratio very near to keilhauite, the 

 whole of the sesquioxyd base is ferric, while a partial replacement of the same kind is 



IX. 



Tribe 8. Protopebadamantoid. 



observed in some varieties of idocrase. Next in order comes garnet, including many 

 species, in some of which ferric or chromic oxyd replaces more or less completely alumina ; 

 while the protoxyd base is either wholly lime or in part magnesia or manganoiis or ferrous 

 oxyd. The single example of garnet given in Table IX is that of a pure lime-alumina 

 sijecies examined by the writer. We have placed allanite near to garnet for the reason 

 that, according to Rammelsberg, the best determinations give approximately the garnet- 

 ratio, 1:1:2, rather than that of epidote, 1:2:3, notwithstanding that the species is 



