PRESSUEE IN BTEATIEIED PALEOZOIC E0CK8. 19 



Seeing, then, that the rocks thus affected by " regional meta- 

 morphism," in the full and complete sense of that term, are 

 proved to be, in many cases, pre-Cambrian, and that in no case 

 has the asserted Palaeozoic ago of sach rocks been satisfactorily 

 determined, it seems reasonable to infer that their environment 

 at the time of change was one which has rarely, if ever, recurred, 

 and that it is possible to state the " uniformitarian " doctrine so 

 unguardedly as to lead to conclusions which are not warranted 

 by the facts of nature. 



How far, then, may we take foliation as an indication of original 

 stratification ? Certa^'nly not in all cases. I have already called 

 attention to some instances requiring a different interpretation, 

 but I believe that the distinction of these is often possible. When 

 I am able to lay before the Society the full results of my work in 

 the Alps last summer, which I trust will be before the conclusion 

 of the present session, I have good hopes of advancing nearer to 

 giving an answer to this question. 



EXPLANATION OF PLATE II. 



Fig. 1. Banded Phyllite from near Morlaix. x 27. 



Eepresents the interbanded quartzose and darker micaceous layers, 

 as described in the text (p. 12), the latter predominating in the draw- 

 ing. The " embryonic" foliation can be seen running diagonally across 

 the drawing from about N.N.W. to S.S.E., but much waved and 

 puckered; the upper dark band shows distinctly the lines of the 

 strainslip-cleavage running about N.N.E. 



Fig. 2. Effect of contact-metamorphism on a banded phyllite from the road 

 to Huelgoat, 8-5 kil. from Morlaix. x27. 



Eepresents the interbanded quartzose and micaceous layers, as 

 described in the text (p. 14), the former predominating in the draw- 

 ing ; the greater size of the flakes of mica and granules of quartz 

 throughout and the diminished opacity of the darker band are indi- 

 cated. This part of the slide does not show the " soldered-up " lines 

 of strainslip-cleavage, which, however, may be seen in another part. 



(For the Discussion on this paper, see p. 45.) 



o2 



