28 THE CANADIAN NATURALIST. [Feb. 



and specific gravity which show them to belong to orthoclase, rather 

 than toalbite. The anorthic feldspars offer in their composition such 

 gradations from albite to anorthite, that the various intermediate 

 species which have been distinguished seem to pass into each 

 other. (Silliman's Journal [2], xviii, 2V0,Phil. Mag. [4],ix, 262.) 



Next to the feldspars in lithological importance are the two 

 species, pyroxene and hornblende. These are sometimes found 

 associated in the same rock, and the varieties of pyroxene known 

 as diallage and smaragdite are frequently surrounded or penetra- 

 ted by horublende. This association of the two species should be 

 kept in mind, inasmuch as the substitution of pyroxene for horn- 

 blende in anorthosites, has been made the basis of a subdivision in 

 classification. (Silliman's Journal [2], xxvii, 339.) Among the micas 

 found in silicated rocks, besides muscovite and a magnesian mica 

 (phlogopite or biotite), are to be included the hydrated micas 

 observed by Haughton in many of the Irish granites. Of these the 

 one is margarodite, and the other a uniaxial black mica, also hydra- 

 ted, which he has referred to lepidomelane. (Trans. Royal Irish 

 Acad., xxiii, 593.) The presence of from four to six hundredths of 

 water in the micas of these granites is important in conneation with 

 ^ the evidence already given of the intervention of water in the for- 

 mation of granitic rocks. These two hydrous micas were often 

 found by Haughton to be united in the same crystal ; and Rose has 

 remarked a similar association of potash-mica and magnesian mica 

 in certain granites. (Senft, die Felsarten, p. 206.) 



A scientific nomenclature for compound rocks presents such 

 great diflBculties that we must be content for the most part with 

 trivial names which have from time to time imposed. In the case 

 of simple rocks, the terms quartzite, pyroxenite,anorthosite, and or- 

 thoclasite are sufficiently definite, or they may be farther charac- 

 terized as normal orthoclasite, etc.; while quartzose, micaceous, 

 and quartzo-micaceo-hornblendic orthoclasite would designate 

 various compound rocks of which orthoclase is the base. Such 

 names, however descriptive, will never replace the older terms 

 granite, syenite, etc., which are employed to designate certain 

 forms of orthosite rocks. The frequent association of a triclinic 

 feldspar (oligoclase) with orthoclase in granite rocks, and the par- 

 tial or total replacement of the micas generally present in these, by 

 hornblende, by chlorite, or by talc, giving rise in the latter case 

 to what is called protogine, are well known. Nepheline (elaeo- 



