46 THOMAS STERRY HUNT OX A NATURAL SYSTEM IN 



erase, garnet, beryl, enclase. ardonuite, axiiiite, epidote, spodumene, sapp>hiriiie, staiirolite, 

 and the tonrmalines ; besides allauite, the titanic species, keilhauite and schorlomite, and 

 the remarkable ferric species, œgirite, acmite and arfredsonite. These, though differing in 

 this regard among themselves, have all of them a more condensed molecule than the 

 densest of the spathoids, and it is to be noted that their resistance to acids is correspond- 

 ingly greater. The highlj' basic adamautoids of this suborder, such as garnet, epidote 

 and zoisite are not attacked, while the basic spathoids (as scapolites and feldspars) are 

 readily decomposed, by acids. The phylloid type in this suborder is represented by the 

 great group of the micas and chlorites, constituting the tribe of Protoperphijlloids and 

 including a large number of species, both hydrous and anhydrous, which are more 

 condensed than the spathoids, though less so than the adamautoids. 



In the fifth place we find the uncrystalline colloidal species of this suborder repre- 

 sented by the tribe of the Pinifoirh, named for the typical species, piuite, and correspond- 

 ing to the ophitoids, with which they have many analogies. This tribe includes several 

 species which are essentially hydrous silicates of alumina, with more or less alkali. 

 With the true piuitoids are probably confounded other substances which are compact 

 forms of the corresponding phylloids. The hydrous silicates palagonite and pitchstone, 

 and the anhydrous tachylite and obsidian, though not definite mineral species, are placed 

 in this tribe, as being colloidal protopersilicates. 



§ 53. The hydrospathoid and spathoid tribes are scarcely represented among the less 

 protobasic silicates of the second suborder, and with the exception of westauite, which 

 seems to be a hydrospathoid, are as yet unrecognized in the suborder of the Persilicates. 

 The Peradamaniokh, however, constitute an important tribe, including andalusite, topaz, 

 dumortierite, fibrolite, xenolite, cyanite and the zircons. The Perphylloid tribe is repre- 

 sented by a few micaceous species, such as pholerite, talcosite, kaolinite and pyrophyl- 

 lite ; while the uncrystalline or colloid type in this suborder, which we have designated 

 the ArgiUoid tribe, includes the various clays or amorphous hydrous silicates of alumina, 

 from schrotterite through allophane and halloysite to cimolite and smectite, together with 

 wolchonskoite and chloropal. 



§ 54. In the preceding scheme it will be seen that the first place has been given to 

 the great chemical distinctions which are embodied in the three suborders of silicates. 

 It might be thought that the well-marked physical types which we have seen recurring 

 in the different suborders should be made the ground of a first subdivision of the order 

 Silicate, rather than the chemical distinctions here adopted. These resemblances, depend- 

 ant upon similar molecular aggregations and upon p)hysical structure are, however, less 

 fundamental than those based upon elemental constitution, which, as we endeavored to 

 show, are genetic, and should, therefore, have assigned to them a greater significance than 

 those analogies based on similarity of aggregation and structure, which although of much 

 importance in classification, are essentially mimetic. The foundations alike of the order 

 and the suborders are wholly chemical, and the division of each of the suborders into 

 tribes is primarily and essentially chemical and genetic. On the other hand, the remark- 

 able resemblances between the corresponding tribes in the different suborders, which are 

 chemically distinct, is imitative or mimetic, and should, therefore, be assigned a sub- 

 ordinate rank in classification. 



§ 55. In arranging still further the different families, genera, and species, in each tribe, 



