2i8 HOLLAND: CHARNOCKITE SERIES. 



In some of the basic types, the norites, we come across lenses 

 or bands from which all felspar has been excluded, and the rock is 

 composed of augite, hypersthene and hornblende, with sometimes 

 small quantities of olivine, iron-ores and green spinel (Nos. 11*891, 

 11*904). But in all these cases microscopic sections across the 

 junction of the ultra-basic schliere and the less basic main-mass 

 show no sharp line of division (specimen 9*667). 



The early-formed basic material may be broken into by the 



residual magma and divided into angular 



Primary eruptive breccia. ° 



fragments, which, cemented by the more acid 

 subsequently intruded magma, give the rock the appearance of a 

 breccia — the Primarbreccia of Sederholm and Primdrtrumer of 

 Lossen. Sometimes we merely meet with isolated fragments of the 

 basic rock floating in the general main-mass ; at other times the 

 fragments of basic rock are separated by thin films of the acid 

 variety, and at other times again an exposure may show about equal 

 quantities of the basic fragments and more acid cement. 



The late Prof. G. H. Williams proposed to use the term proto- 

 clastic structure for these phenomena. 1 This term has, however, 

 been used in a slightly different sense by Brogger for describing 

 the elaeolite-syenite of South Norway, in which the mineral con- 

 stituents have sometimes been crushed and broken by movement 

 during the process of consolidation, the granulation being often 

 accompanied by foliation and the production of eye-structure 

 (primare Augenstructur). The use of the term primary breccia y 

 or more fully primary eruptive breccia, in imitation of Lossen and 

 Sederholm, instead of the term protoclastic structure, will thus 

 reduce the chances of confusion, and at the same time clearly 

 express the nature of the phenomenon under consideration. A 



1 Fifteenth Ann. Rep., U. S. Geol. Surv., 1893-94, p. 662. " We know that basic 



secretions are a common feature of slowly solidifying granitic magmas, while a partially 

 solidified portion of such a mass may be broken into and brecciated by a subsequent intru- 

 sion of the residual magma, whose composition has slightly changed, thus producing a sort 

 of protoclastic structure" (" Criteria for the recognition of ancient plutonic rocks in highly 

 metamorphosed terra nes ", G. H. Williams). 

 ( IOO ) 



