SUMMARY AND CONCLUSIONS 333 



The femic minerals are practically negligible in the three persalanes 

 (I, III, and IV), but are present in large amounts in dosalane (II) and 

 in the three salfemanes (V, VI, and VII). Olivine and diopside are 

 present in each of the salfemanes, but vary within rather wide limits. 

 Magnetite, ilmenite, and apatite, the magnetite always dominant, are 

 present in each norm in small amounts in the persalanes, but more abun- 

 dant in the salfemanes. 



MINERALOGICAL CHARACTERS 



No single mineral as an essential constituent of the rocks occurs in all 

 types recognized in the region, but several are present in widely different 

 amounts in all the rocks, varying as to the relation of felsic and mafic 

 constituents. 



Quartz actually occurs as a constituent. in only two of the rock types, 

 the persalane toscanose and the dosalane tonalose, the general character 

 of the magmas representing the other types being such as to preclude its 

 presence. The feldspars, orthoclase and plagioclase, may be regarded as 

 persistent minerals, since they form large but varying percentages in all 

 the rocks. Orthoclase is developed as an essential component of each 

 type except the salfemane, auvergnose, in which it is noted only as a very 

 minor accessory. Plagioclase, in large but varying percentages, ranges 

 from the sodic variety, albite, in toscanose to the sodic-calcic varieties in 

 the six remaining types. Nephelite and analcite are developed as prin- 

 cipal components of miaskose, monchiquose, and ourose, the former being 

 limited to miaskose and the latter to monchiquose and ourose. 



Of the mafic minerals biotite is perhaps the most persistent, being a 

 component of all types, but is only of quantitative importance in monchi- 

 quose and ourose. Augite is present in large amount in dosalane (II) 

 and in the salfemanes (V, VI, and VII), and is sparingly developed in 

 the persalanes (I, III, and IV). Hornblende is essentially absent from 

 the rocks of the entire region, except in the closely related group of dikes 

 (miaskose, monchiquose, and ourose) in the northern part of Augusta 

 County, where it is most abundant in monchiquose and is developed only 

 as a minor constituent of miaskose and ourose. Olivine as a modal min- 

 eral is limited exclusively to auvergnose, it being present in every speci- 

 men of this type studied. 



The lesser minerals, developed only as microscopic accessories, exercise 

 no important influence on the character of the rocks and need not be 

 discussed. 



TEXTVRAL CHARACTERS 



The rocks of the region are all intrusive, occurring without exception 

 as dikes; aw noncrystalline, and range in granularity from medium 



