Rev. J. F. Blake — The Llanheris Unconformity. 177 



in a conglomerate. It is not positively stated that these observations 

 are incorrect, but only that " we took the dip on several blocks and 

 surfaces, of which four at least were clearly shown varying from 

 15°-25° generally to the S. of E. or S.E." ; from which it is left to 

 be inferi-ed that these statements are incompatible with mine. 

 But they are not. I have seen " blocks and surfaces " showing, 

 the dips mentioned, but they are isolated blocks lying on the 

 eastern slope of the hill, and it is not certain that they are in situ. 

 I did not even look for dips on such blocks, as dips are worse than 

 useless unless the rocks are certainly in situ. But even in that case 

 these dips, combined with the more persistent ones of the crags, 

 would not affect my argument to any material extent. But with 

 such rocks as these, and so exposed on the slopes of a rounded hill, 

 it is not by isolated dips, which are liable to all kinds of accidents, 

 but by the direction of the outcrops that the strike may best be 

 determined. In this case, if we walk on a level line round the base 

 of the north side of the hill a little above the pathway, we keep on 

 conglomerate, but if we anywhere mount a little and take another 

 contour-line, we keep upon grits. This would indicate that the 

 junction between them, i.e. l»edding of both, was not far removed 

 from the horizontal in a direction across the hill. 



The further remarks about this district are— (1) That the con- 

 glomerate of the lower crags is not like that of the summit, as it 

 does not contain the large slate pebbles. It is true that the pebbles 

 of cleaved rock with the appearance of slate are not so large as in 

 the latter, but there are many of them. (2) That whereas I said 

 of a certain area that it was all covered with conglomerate and grit, 

 in fact no small part consists of unbroken sward. This is only true 

 of that part which I called " the lower slopes," and which I dis- 

 tinguished from the part all covered with conglomerate and grit. 

 (3) That it is remarkable that the conglomerate, if unconformable, 

 does not spread over on to the purple slates. This has not been 

 proved to be the case, and if true is easily explained. The fault 

 which bounds the purple slates is probably a thrust-plane which lifted 

 them and their covering above the level of the conglomerate on the 

 other side, and they have been worn back to that level by denudation, 

 which necessarily first removed the conglomerate. Probably also 

 ice has swept all debris away. 



In this district, then, my critics have brought no valid objections 

 against my conclusions, and have failed to propose any reasonable 

 alternative. Meanwhile they have not touched the argument from 

 the great spread of the conglomerate and its associates over a very 

 wide area on the surface of the hill, while nothing but a 3 feet band 

 is found in the adit,^ nor the still more cogent argument that, whereas 

 the conglomerate here lies on, or is next to, a great mass of banded 

 slate, in the neighbouring hill of Mynydd-y-cilgwyn it lies entirely 

 on felsite, and continues round to the western side of it. 



^ I might add that this is not quite like the summit conglomerate, hut such 

 arguments are of little value. 



DECADB IV. — VOL. Y. — NO. IV. 12 



