THE METAMORPHIC ROCKS OF ADELIE LAND. 8TILLWELL. 107 



It is recorded (p. 20) that there are certain zones or belts in the serpentine which 

 have a rudely concentric arrangement. This zoned character is stated (p. 21) to be 

 " clear evidence that the serpentine is an intrusive stock that welled up and forced 

 outwards the surrounding schists." In this it seems that the very metamorphic imprint 

 of the mass is turned into evidence of intrusion. The metamorphic character of the 

 Lizard serpentine is more or less affirmed by Flett when he says (p. 70) that the 

 microscopic examination shows that very few specimens can be described as normal 

 igneous rocks ; that the normal poikilitic association of olivine and pyroxene is absent 

 except for traces in the least modified bastite serpentine or " weathered Iherzolite " ; 

 that the large pyroxene crystals are commonly broken or have their cleavage planes 

 twisted ; that tremolite is found to increase in quantity hand in hand with the 

 development of foliation and augen structure. As tremolite is a well-known 

 metamorphic mineral, the zone of tremolite serpentine may very well be but one phase 

 of the metamorphic product due to varying metamorphic conditions. The augen 

 structure, the foliation, and the schistose character that is described (p. 69) is strong 

 evidence of the metamorphic, not weathered, character of the rock. The absence of 

 foliation and schistosity in some parts of the serpentine body is no evidence to the 

 contrary, as massive textures are common among the crystalline schists. Further, 

 the serpentine has been demonstrated by Flett (p. 120) to be earlier in age* than the 

 group of rocks styled " Kennack Gneisses," which bear the very marked individuality 

 of typical crystalline schists. These schist characters have been impressed by certain 

 external metamorphosing conditions, and it is not reasonable to suppose that 

 the peridotite, surrounded now by metamorphic rocks, has escaped the whole of these 

 forces. If, then, the serpentine be acknowledged to be a primary metamorphic product 

 in any occurrence at all, it is reasonable to concede that the Lizard serpentine is likewise 

 a metamorphic product, and should therefore be treated primarily as such. If the 

 water content of serpentine is considered a barrier to the hypothesis, it must be 

 remembered that Grubenmann postulates considerable water in his epi zone of meta- 

 morphism in which hydrous minerals like chlorite are common. 



Throughout the memoir there are frequent references to fluxion banding in the 

 serpentine in the so-called gabbros, and in the Kennack gneisses. Now, fluxion 

 structures are true igneous structures developed by movement in the magma during 

 consolidation. If they appear in metamorphic rocks they can only do so as 

 relic structures, and if the decrystallisation during metamorphism is intense, fluxion 

 structure will be very difficult to recognise. It therefore becomes incumbent to examine 

 the evidence put forward in order to discover if a different aspect will create a different 

 interpretation. Before doing so, however, we will more fully explain the standpoint 

 from which the question is approached. 



* In a later publication, " The Crystalline Rocks of the Lizard," issued as a pamphlet by Bowes and Bowes, Cambridge, 

 Prof. Bonney doos not accept this opinion of Flett's and insists on his own former interpretation, viz., that the Kennack 

 gneisses are older than the serpentine. Whether Bonney be correct or not, the argument remains unaffected, as far as the 

 Survey memoir is concerned. 



