186 PETROGRAPHICAL ABSTRACTS AND REVIEWS 



nian albitophyres, in the form of breccia and tuffs, with phenocrysts of 

 albite, orthoclase, microperthite, and rarely of brown hornblende, in a 

 groundmass of albite microlites. In the quantitative system these 

 belong to dacose, andose, and subrang 5 of dacose, not named nor even 

 represented by analyses when that system was published. (2) Carbon- 

 iferous orthophyres, also in the form of tuffs and breccias. The pheno- 

 crysts are of orthoclase, albite, and in some cases anorthoclase ; the 

 groundmasses where crystalline are of orthoclase microlites and poikilitic 

 quartz; some are glassy and perlitic. They belong to alaskose, liparose, 

 and the unnamed subrang I (perpotassic) of alaskose. (3) "Micro- 

 granulitic tuffs," consisting of fragments of andesine, bipyramidal quartz, 

 and biotite in a chalcedonic cement. These are water laid and appar- 

 ently not of purely volcanic material. They belong to toscanose and 

 are more limy than the albitophyres. (4) "Microgranulites." Some 

 of the rocks thus designated are hypabyssal, others, passing into "por- 

 phyre petrosilicieux," are thick, devitrified rhyolitic flows. An analysis 

 of the hypabyssal rock is that of a toscanose, while the two specimens 

 analyzed of the extrusive rock are alaskose and liparose. (5) Lampro- 

 phyres. These also occur partly as thin dikes and partly as flows. 

 The dike rocks have phenocrysts of biotite and pyroxene in a ground- 

 mass of orthoclase, plagioclase, and biotite; the lavas have phenocrysts 

 of olivine, augite, and sometimes hypersthene, in a groundmass of 

 plagioclase, orthoclase, and sometimes biotite. In the quantitative 

 classification, they are harzose, shoshonose, and auruncose. Chemically 

 both extrusive and intrusive "lamprophyres" are characterized by 

 richness in potash, resembling in this respect the porphyritic granite 

 from which they are supposed to be differentiates. 



The author summarizes the chemical data by estimating the average 

 composition of each group of rocks and of all the rocks together excepting 

 the diorites, albitophyres, and granulites. With these exceptions, all 

 are markedly consanguineous, and the general average composition has 

 in the scheme of Michel-Levy the same "magmatic parameters" as the 

 granite supposed to be the " mother-rock." 



The albitophyres, by their richness in soda, are in remarkable con- 

 trast to the other rocks, in which dominance of potash is general. It is 

 a striking circumstance that names are wanting in our quantitative 

 classification for two of the albitophyres because of their unusual richness 

 in soda, and' for two other rocks — an orthophyre and a lamprophyre — 

 because of their unusual richness in potash. 



F. C. Calkins 



