I30 HOLLAND: CHARNOCKITE SERIES. 



consolidation ; but as such a system must always separate rocks that 

 are magma relatives, and bring together others that have no genetic 

 relationship, it falls short of the requirements of the geological surveyor. 

 For the wider problems of geology it is necessary that we should know 

 how to subordinate the accidental differences to the general family like- 

 nesses between rocks, to group together, in fact, those which have 

 been produced by the same geological effort, and which form a 

 geological unit. In other words, the geological surveyor is more 

 concerned with the delimitations of the petrographical provinces 

 represented within his country than with the mere cataloguing of 

 lithical varieties. 1 



Whilst, therefore, we group together, and map as one form- 

 ation, a number of diverse varieties of rocks (which are true com- 

 patriots within this petrographical province) under the name 

 charnockite series^ the various constituents of this formation may 

 be distinguished from one another by the ordinary names used for 

 equivalent mineralogical aggregates. As we believe the charnockite 

 series to be igneous in origin and to present intrusive relations to 

 their older neighbours, the terms used for the rock varieties within 

 the group are those commonly used for mineralogically similar 

 ioneous rocks. Thus the types which are composed essentially of 

 hypersthene and plagioclase are nontes } and, according to the ferro- 

 magnesian silicate associated with the rhombic pyroxene, we may 

 have augite-norites, hornblende-norites, or mica-norites. The acid 

 form, composed of quartz, microcline, hypersthene and accessory 

 iron-ores, is strictly a hy per sthene-gr anite or charnockite^ and 

 the non-felspathic forms, composed almost wholly of pyroxenes, are 

 pyroxenites? 



1 Prof. Judd was perhaps the first to show by a ground-work of accurately deter- 

 mined penological and geological data that there is a recognisable set of family charac- 

 teristics {consanguinity, Iddings ; BZutverwandschaf-, Brogger^ presented by igneous rocks 

 which, within a limited geographical area, have been formed at a definite geological period, 

 and he expressed these facts by considering such rocks to be members of a petrographical 

 province. Quart. Journ. Geol. Sac, Vol. XLII (1886), p. 54. 



» The term pyroxenite has been used in several totally distinct and unrelated senses, but 

 is now more generally used for eruptive pyroxene rocks. 



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