504 



ME. E. EUTLET ON" THE EOCKS 



the direction of the micaceous bands, as already pointed out in the 

 descriptions of specimens jSTos. 22 and 26. That the direction of 

 these streams of enclosures is dependent upon causes operating sub- 

 sequently to the formation of the quartz is evident from the fact 

 that when the section is examined in polarized light the same 

 stream of enclosures will be found to traverse without deflection 

 several crystals which differ from one another in optical orienta- 

 tion. 



The rock is a biotite gneiss. 



No. 30. Raggedstone Hill, Eastern Spur, North end, top. — A very 

 fine-grained, pale, bluish-grey rock, resembling an exceedingly fine- 

 grained quartzite. The rock is very hard, a knife-point making 

 little or no impression on it. 



Under the microscope, between crossed nicols, the section presents 

 a general appearance similar to that of the ground-mass of a quartz- 

 porphyry, or of a rather coarse microcrystalline felsite, in which 

 occur numerous porphyritic crystals of felspar and delicate strings 

 and specks of more or less opaque granular matter, which, under 

 reflected light, appears of a yellow-white or pale reddish-brown 

 colour. Under a higher power, however, it is seen that the opacity 

 of these strings and spots is only partial, and that in great part 

 they consist of small translucent greenish or nearly colourless 

 granules of epidote, with much fine dusty matter of a deep green 

 colour, which appears to be allied to chlorite. The porphyritic 

 felspar seems to be of a mixed character, the angles of extinction in 

 some crystals being apparently very low, in other cases approxi- 

 mating to those of labradorite. Microcline is also present. Some 

 of the felspar may be andesine. 



The rock in some respects resembles granulite, but garnets are 

 absent, and the felspar is all, or nearly all, plagioclastic. On the 

 other hand, it is not unlike some felsites, especially some of the 

 more coarsely micro-crystalline parts of certain devi trifled rocks. 

 I am, however, inclined to regard it as an altered sandstone derived 

 from the disintegration of the older Archaean rocks, and bearing 

 the same relation to them that arkose or millstone-grit bears to 

 granite. 



A drawing made from a section of this rock, magnified 25 diame- 

 ters, is given on PI. XXI. fig. 1. 



No. 31. Haggedstone Hill, Eastern Spur, Worth end, top. — A pale 

 brownish-grey to bluish-grey rock, resembling quartzite strongly 

 impregnated with very minute silvery-looking micaceous scales,, 

 and with a schistose structure. 



Under the microscope, in polarized light, this rock is seen to be 

 essentially a quartzite, in which a schistose structure is induced by 

 extremely thin micaceous or sericitic films. These are, in some 

 instances, crossed by rather irregular and tolerably broad bands, 

 consisting of quartzite of a much finer texture than that constituting 

 the mass of the rock, and suggesting that another stress has been 

 experienced in a direction approximately at right angles to that 



