ON THK CRYSTALLINK ROCKS OF THE LIZARD DISTKICT. 475 



by slight strains, either in cooling or in the alteration of the 

 olivine constituent into serpentine. At Lawarnick Pit, near 

 Kynance Cove, a faint banding is often perceptible iu the compact 

 serpentine, and a like structure is often developed rather conspicu- 

 ously on the weathered surfaces of the rock, both in the neighbour- 

 hood inland and for some distance along the coast to the north. 

 This structure commonly has a roughly uniform strike, and thus 

 might naturally be interpreted as a result of pressure ; but we noted 

 variations in this district from a little W. of N., round by W. to 

 W.S.W. The rock also is not rendered fissile by it. So, if a 

 pressure structure, it is certainly anterior to serpentinization. 



On the east coast this structure is much more rare and local. It 

 may not seldom be detected on slightly weathered surfaces in the 

 black serpentine S. of Kennack Cove, but the rock under the micro- 

 scope does not give any indication of having suffered from a general 

 crushing. Near Compass Cove we observed a sheet of compact- 

 looking serpentine, from 4" to 8" across, in the ordinary serpentine ; 

 the latter being one of the usual red serpentines with fairly conspi- 

 cuous but rather altered bastite-grains. This mineral also occurs 

 in the former, but much more sparsely (being sometimes absent), 

 and in grains less than half the diameter of the other. The compact 

 rock under the microscope does not, hoAvever, show any sign of 

 crushing, and presents the usual structures ; indeed, the presence 

 or absence of bastite is the main difference between the two slides. 



On the E. side of Lankiddcn Cove, a rather compact serpentine 

 exhibits grains of an iron oxide arranged in lines rudeh' parallel, 

 and in the middle is a band about 4" wide, with a slightly streaky 

 structure, containing bastite ; the dominant colour in both being a 

 greenish grey. Neither the grains of iron oxide, probably chromite, 

 nor of bastite, in the latter, show any signs of crushing. The 

 former indicates, by the parallelism of the " strings " of opacite, 

 and the arrangement of the " rootlets " of flaky serpentine, that 

 there has been originally a somewhat parallel arrangement of the 

 olivine grains, but the resemblance is far greater to a fluxion- than 

 to a crush-structure. A similar structure was noted in a second 

 locality, but the serpentine generally is normal. 



The following extract from Prof. Bonney's diary, describing 

 a visit to the Iherzolite of the Lac de Lherz, written in 187(5 

 (June 27th), indicates the existence of a similar structure in a 

 peridotite, which certainly appears quite free from the effects of 

 dynamo-metamorphism : — "■ Occasionally also a sort of stratified 

 appearance comes out in weathering, just as I have observed in 

 some of the Lizard serpentines. I could not see that this corre- 

 sponded with any marked internal structure." He states, in regard 

 to this, in his account of his visit printed in the ' Geological 

 Magazine ' for Eeb. 1877 *, that the structure, in his opinion, has, 

 like that at the Lizard, " some connexion with an internal paral- 

 lelism," and thinks *' it will prove to be connected with a fluidal 

 structure." 



* Dec. ii. vol. iv. p. GO. 



2k2 



