THE METAMORPHIC ROCKS OF ADELIE LAND. 8TILLWELL. 117 



inclusions and yielding an intermediate rock, we may only have a further example of 

 metamorphic diffusion. In the " Blotched and Streaky Gneisses " the basic material 

 may be again, as in other cases, the fragments of a disrupted and broken dyke. Such a 

 possibility is suggested because this type passes into the " Flow Banded Gneisses," 

 which may be an injection banding which has preserved its entity throughout the 

 metamorphism. 



The granite gneiss, which occurs within the serpentine area and is intrusive into it, 

 would be affected on its margin by the serpentinisation in the same manner as the gabbro 

 dykes and Kennack gneisses. Flett describes (p. 41) how. the older serpentine is often 

 converted for a short distance from the contact into a soft greenish rock consisting 

 mainly of talc and tremolite, with sometimes anthophyllite and chlorite. He considers 

 (p. 142) that these contact phenomena are pneumatolytic changes due to hot vapours 

 and liquids given off by the cooling gneisses. An analysis is quoted to illustrate the 

 difference in composition between the tremolite rock and the serpentine. As, however, 

 tremolite and talc are better known as metamorphic minerals than as pneumatolytic 

 minerals, it is very probable that Flett is dealing with a metamorphic product rather 

 than a pneumatolytic one. The observed difference in composition can be readily 

 explained by metamorphic migration of material. 



Summary. 



I 



The memoir that is criticised contains an account of the extraordinary number of 

 rock types met with in the Southern Lizard. The area is one of exceptional 

 metamorphism, yet it is considered that the study has been approached more from the 

 standpoint of igneous rocks than from the standpoint of metamorphic rocks. This has 

 occurred because the metamorphic rock has not been given the same individuality 

 that is given to igneous and sedimentary rocks. An attempt has been made to state the 

 metamorphic standpoint and to demonstrate the results obtained thereby. 



The Lizard serpentine has been viewed as a metamorphic rock, foliated in part. 

 We think that the term " fluxion banding " is in most cases a misnomer when applied 

 to these metamorphic rocks, and that the term " flowing gneiss " is also founded on 

 misconception. The foliation of the gabbros dykes which penetrate the serpentine 

 can receive adequate explanation from the combined effect of the external 

 metamorphosing forces that cause serpentinisation, and the internal pressure and heat 

 developed by the serpentinisation of the original periodotite. The introduction of the 

 term " injection foliation " is not necessary, and it does not assist the explanation of 

 the remarkable dyke foliation. 



Descriptions in the area have corresponded to the conceptions of metamorphic 

 differentiation and metamorphic diffusion. Transition is observed between the 

 serpentine and the adjacent hornblende schists. Diffusion types are also present in the 

 so-called " intermingling of acid and basic magma " in the complex Kennack gneisses. 



