336 



Transaction*. 



All the conditions for solution and recrystallization were abundantly 

 present in the case under consideration. The intrusion of the norite 

 produced a high state of strain in the porphyry. There is still evidence 

 of this in the strain shadows observable in the feldspar phenocrysts at 

 Tewaewae Point, and the strain must have been much greater in rocks 

 nearer the intrusion. This is shown in the schists by the number of 

 shearing-planes, often but a few inches apart. 



The temperature of the intruded mass must have been very high, 

 and the cooling must have been prolonged, for the norite is holocrystalline 

 and of coarse grain. 



Water would be present in sufficient amount, as percolated meteoric 

 water in the porphyry perhaps, but more probably the supply would be 

 the magmatic waters from the norite itself. 



B. The Origin of the Amphibolite. 



Of amphibolites Harker* says, " The name ( amphibolite ' has often 

 been applied to rocks, usually more or less markedly schistose, in which 

 hornblende is the dominant mineral. Many of them are doubtless the 

 results of dynamic action on diorites, and sometimes on dolerites and 

 gabbros." 



Teallf describes the formation of a hornblende schist from a dolerite 

 (or diabase) from two dykes which occur in the Archaean gneiss of the 

 north-west of Scotland, near the Village of Scour ie. 



A comparison of his analyses with that of the Bluff amphibolite is 

 instructive: — 



Si0 2 



Ti0 2 



A1 2 3 



Fe,0 3 



FeO 



MgO 



CaO 



K 2 



Na 2 



H 2 



CO. 



Totals 



Specific gravity 



3105 



3-111 



A. Dolerite (diabase?), Scourie, north-west Scotland. 



B. Hornblende schist derived from A. 



C. Amphibolite, dyke, Bluff, derived from diabase. 



Teall's conclusions are: "(1) That the hornblende schist of the 

 Scourie dykes has been developed from a dolerite by causes operating 

 after the consolidation of the dolerite, and that the metamorphosis ha^ 



* Harker, A.. " Petrology for Students," 4th ed. (1008), p. 326. 



t Teall, J. J. H., " On the Metamorphosis of Dolerite into Hornblende Schist " 

 Quart. Journ. Geol. Soc, vol. 41 (1885), p. 142. 



