650 



MESSRS. CLOTJGH, MAT/FE, AND BAILEY OK [Nov. I909,. 



before the main line of fault is reached. The crush-rock occupying 

 these minor planes of movement generally measures a few inches 

 across, and has a poorly developed platy structure parallel to its 

 edges ; as a rule, it is so finely ground, that to the naked eye it 

 shows very little evidence of brecciation. The strike of the 

 quartzite is sometimes sharply deflected in the immediate vicinity 

 of these shear-bands ; but sometimes, on the other hand, it is quite 

 abruptly truncated. Although the crush-rock has in all these cases 

 lost every sign of bedding, it is still white and its quartzitic nature 

 is obvious. 



On approaching the main line of movement, the quartzite is 

 again torn out in the manner just described : and a belt is formed 

 of white, crushed, quartzitic rock a couple of feet thick (12329), 

 Beyond this, long tongues of the white rock begin to be isolated in 

 a darker matrix, and in the next stage disintegrate, while the 

 proportion of matrix rapidly increases. The latter possesses an 

 obvious flow-structure which winds round the abundant inclusions, 

 in much the same manner as the banding in the flow-breccias 

 so often found among the rhyolite lavas. Movement has apparently 

 been so intense in this case as to lead to incipient fusion (p. 629). 

 This breccia with flow-banded matrix is a foot wide, and next to it 

 comes the flinty crush-rock (12332), the extreme product of the- 

 disturbance (fig. 8.) 



The last-mentioned 

 rock is only an inch 

 thick. It is most de- 

 licately banded ; and, 

 though it sometimes 

 weathers with a light- 

 coloured crust, when 

 freshly fractured it is 

 quite black, and pos- 

 sesses a semi- vitreous 

 lustre. The only frag- 

 ments visible in it are 

 minute gleaming specks 

 of quartz, which occur 

 in great numbers and 

 are easily discernible 

 with a pocket-lens, as 

 also a few tiny crystals 

 of pink felspar, which 

 are found for the most 

 part close to the junc- 

 tion with the fault- 

 intrusion to the north. 

 All these different 

 zones of crush-rock, 

 with their platy struc- 

 tures and flow-banding, 



Fig. 8. — Diagram of the boundary-fault, as 

 seen in the cliff of Stob Mliic Mhartuin. 



FAULT-INTRUSION 



BEDDED OUARTZ1TES 



