Wild. — Geology of the Bluff. 337 



been accompanied by a molecular rearrangement of the augite ami 

 feldspar ; and (2) that the molecular rearrangement has in certain cases 

 taken place without the development of foliation." 



Other cases of the formation of hornblende schist from igneous rock 

 have been described by Allport,* who, in his summary, expresses the 

 opinion that " hornblende schists may be metamorphosed igneous rocks, 

 some being derived from dolerites or gabbros, while others are very 

 probably foliated diorites." 



These considerations, in conjunction with the chemical ami 

 mineralogical composition and the structure of the rock, suggest that 

 our amphibolite is derived from the metamorphism of a basic igneous 

 rock. Furthermore, at Green Point there actually does occur a basic 

 igneous dyke rock consisting chiefly of augite in process of uralitization, 

 and striking in a direction such as to indicate its identity with the 

 amphibolite of the Lower Harbour series. 



There yet remains to be shown the causes that produced the change 

 to amphibolite. 



Williamsf points out that augite appears to be the stable form at 

 high temperatures and hornblende at low temperatures. The change, 

 therefore, must have been subsequent to the consolidation of the dykes, 

 for at the time of intrusion the temperature would have been too high 

 to admit of the formation of hornblende. 



We have, therefore, to supply some conditions such as would facilitate 

 molecular readjustment in the augite crystals after consolidation. Such 

 conditions would certainly attend the intrusion of the norite. We need 

 not assume, however, that the intrusion of the plutonic mass at once 

 produced uralitization of the augite. On the contrary, the heat attend- 

 ing the intrusion may have been so high as to prohibit the formation of 

 hornblende. The important point is that a state of strain was induced 

 throughout the whole intruded mass. Evidence in support of this 

 statement has been given above. This condition of strain would con- 

 tinue to exist after the consolidation of the norite, and when the 

 temperature had again fallen to normal. Then would commence the 

 process of uralitization, and it would be assisted by the percolating 

 waters that aided in the metamorphism of the porphyry. 



The conclusions here are, therefore, similar to those of Teall in the 

 case of the Scourie dykes. The amphibolite is derived from a diabasic 

 rock by metamorphism that most probably acted after the consolidation 

 of the diabase, and was accompanied by a molecular readjustment of the 

 augite. 



C . Relative Age of the Rocks. 



The porphyry and the rocks derived from it — that is, the hornblende 

 schists — are the oldest rocks, for into them the other rocks have been 

 intruded. 



Of the intrusive rocks, we assume that the diabasic dykes are older 

 than the norite, for the diabase is metamorphosed to an amphibolite, and 

 the metamorphism is presumably connected with the intrusion of the 

 norite. 



* Allport, " On the Metamorphic Rocks surrounding the Land's End Mass of 

 Granite," Quart. Journ. Geo]. Soc., vol. 32 (1876), p. 407. 



+ Williams, G. H., Am. Journ. Sci.. vol. 28 (1884), p. 259. 



