PROF. A. H. GREEN ON A SECTION NEAR LLANBERTS. 



75 



grey, with very smooth fracture 

 not unlike that of the felsite, but 

 the rock is soft enough to be 

 scratched by the knife and slightly 

 soapy to the touch : it contains 

 many blebs of quartz and fragments 

 of other minerals and rocks, all very 

 much altered : it is very decidedly, 

 but rudely, cleaved, and the clea- 

 vage-planes bend in a wavy way 

 round the fragments. The surfaces 

 bounding this band of rock are 

 parallel to the laminae of the rock 

 A. The rock C, that comes next, 

 is a breccia with a dark grey ma- 

 trix; the fragments are all flat- 

 tened and lie with their flat faces in 

 the same direction ; there is a rude 

 wavy cleavage with a tendency to 

 bend round the fragments. We 

 have here then three bands of 

 rock, all differing in lithological 

 character and separated from one 

 another by parallel and nearly 

 vertical planes ; one of these bands 

 (A) is made up of numerous 

 laminae, each differing from its 

 neighbour in composition, and these 

 laminae are aU parallel to one 

 another and to the planes which 

 separate A from B, and B from C. 

 These facts, it seems to me, admit 

 of only one interpretation. The 

 rocks are bedded and in a nearly 

 vertical position ; there is clea- 

 vage as well, and the cleavage and 

 bedding coincide ; but while the 

 flakiness of the rocks B and C is 

 due to rude cleavage, the plane 

 separating these rocks from one 

 another, the plane separating B 

 from A, and the planes of lamina- 

 tion in A must, I think, be planes 

 of bedding. 



These flaky rocks occupy the 

 whole face of the cutting for a space 

 of about twenty yards, but towards 

 the north-west end a capping of 

 conglomerate comes on above them. 

 The junction slopes down to the 





" |- Quartz-felsite. i^ 



-Conglomerate. 

 -Dyke. 



G-rits with some 

 slaty beds. 



-Dyke. 



.Grits. 



.Dyke. 



21 



i 



Dyke in con- 

 glomerate. 



..Grit. 



Conglomerate 

 and breccia. 



._MassiTe grit. 



Slate. 



0^* 



So 



O <: — I 



^ 

 -§ 





f 

 I- 



