220 Rev. J. F. Blake — The Llanheris Unconformity. 



We will commence with the tramway section. Of this Professor 

 Bonney gave a diagram in C He and Miss Raisin now give 

 a second, and they say, " we adhere to our original diagram." If 

 anyone will take the trouble to put these two diagrams (A and B) 

 side by side and compare them, he will notice that (1) in A a fault is 

 placed betv/een the felsite and the conglomerate, in B it is shifted to 

 the other side of the conglomerate; (2) in A purple slate is repre- 

 sented as occurring in the synclinal, in B there is none ; (3) in A 

 the middle conglomerate is undivided, in B it is divided into two; 



(4) in A the beds between the second and third conglomerate are 

 called green slaty grit, in B they are quite differently described ; 



(5) in A these beds are represented as forming an anticlinal, making 

 the second and third conglomerates parts of the same bed, in B these 

 beds ai'e all made to dip towards the second conglomerate, making 

 the third a distinct and lower bed. When, then, the authors claim 

 that they adhere to the original diagram, and add, " but would shift 

 the anticlinal so as to fall nearly on the third conglomerate," they 

 might as well have said, " but change it altogether." 



I do not complain of a change of views, if frankly acknowledged, 

 but in this case I fear it is a change for the worse, for it lands them 

 in many difficulties. The Cambrian conglomerate has gone by the 

 board, and they have become quite lavish of their successive con- 

 glomerates. They have already claimed one below that on the 

 summit of Moel Tryfaen, and one above that next the felsite by the 

 Llyn Padarn inlet, and here there must be a fourth unless they can 

 account for the change of material lying between the supposed two 

 on one side of the lake, and the two on the other. This material in 

 one case is felsitic grit and purple slate, and in the other felsitic 

 grit of a different kind and " rainspot breccia." Next they have to 

 account for the absence of the second conglomerate on the north-west 

 side of the banded-slate synclinal, and to this end have to inti'oduce 

 a new hypothetical fault for which there is no independent evidence, 

 but rather the reverse. Then they have to deny the identity of the 

 very similar conglomerates in the two crags almost facing each other 

 on the slopes of Y Bigl, on the sole ground that one of them contains 

 additional varieties of pebble. At the same time they identify one 

 of these, on the west of Moel Goronwy, with a totally different 

 felsitic breccia, containing none of the great pebbles, on the east side. 

 They have to make two conglomerates along the west side of that 

 hill, where they acknowledge not to have examined the ground, and 

 where there is certainly only one ; and they draw the second con- 

 glomerate in a straight band right over the high ground, thereby 

 representing it as vertical, though in the tramway section they state 

 that it has a moderate dip. 



There is, however, direct evidence that these second and third 

 conglomerates are parts of one and the same sheet, for one can be 

 traced round on the slopes above the section, passing across about 

 the level of the lower road, with a very narrow interval of grass, 

 into the othei-. This, while it negatives the new section, does not 

 prove an unconformity ; for if, as Professor Bonney originally 



