THE METAMORPH1C ROCKS OF ADEL1E LAND. STILLWELL. 99 



3. Those derived by the metamorphism of impure bands in the limestone series 



(a) Those which are described as " pyroxene hornblende gneiss " or 

 " pyroxene hornblende granulite." 



(6) Those which are described as " feather amphibolite." 

 (c) Those which contain orthorhombic amphibole. 



The amphibolites of igneous dyke origin are recognised when they are found in the 

 field to cut across the bedded white crystalline limestone. Adams and Barlow find 

 that the field evidence is essential to recognise the igneous origin with certainty, but 

 other cases which are macroscopically identical with the established dykes, and which 

 appear interbanded with crystalline dolomite or crystalline limestone, are also considered 

 to be probably igneous. A chemical analysis is quoted, and it is stated (p. 161) that 

 it is highly probable that they were diabases. It is interesting to note that this altered 

 Canadian diabase and the typical amphibolite (No. 629) from Cape Denison are so 

 strikingly similar that they occupy the same division of the American classification. 



Adams and Barlow have assured themselves that amphibolites are formed by the 

 second method by a study of the contact phenomena in the border zones of the granite 

 gneiss. Where the granite has intruded limestone the changes produced are divided 

 into two classes (p. 87) 



1. Alteration of the limestone into masses of scapolite-bearing pyroxene rock. 



2. Alteration into pyroxene gneiss or amphibolite. 



The No. 1 change is proved by finding all possible transitions between the pure limestone 

 and the pyroxenite, which is stated to occur (p. 88) at or near the contact with the 

 granite. With simple contact metamorphism we expect to find in a traverse across the 

 boundary transition from limestone to pyroxenite and then a sudden change from 

 pyroxenite to granite. This seems to be indicated, and the varying nature of the product 

 in a measure supports the theory ; but it needs to be demonstrated that the same 

 metamorphism which affected the granite after its consolidation would not produce 

 the observed results in the limestone. The contact alteration is considered to be of the 

 pneumatolytic type, but it is difficult to understand how such would produce the biotite 

 rock (p. 93) or the felspar scapolite rock (p. 94). It is stated that the field relations 

 of these two rocks to the limestone in Harcourt and Dudley (p. 96) render it almost 

 certain that they are produced by the alteration of the limestone. 



The second change is found (p. 97) " where granitic magma shatters the invaded 

 rocks and floats away the fragments in its moving mass." It may be pointed out that 

 not only is such an idea opposed to the present day conceptions of the manner in which 

 holocrystalline rocks of coarse granularity arise, but it only permits heat as the 

 metamorphic agent. These inclusions are stated to be similar to those which are 

 described in the granite gneiss at great distance from the junction with the limestone. 

 It is stated (p. 98) that the field evidence is scarcely susceptible of any interpretation 



