34 



ON THE GEOLOGY OF THE DISTRICT. 



Bt Dr. M'Cullo0oh. 



Gentlemen, — We are now placed not far from the centre of that great mass 

 of the Old Red Sandstone which forma the principal part of the counties of 

 Hereford, Monmouth, and Brecon, and from the point where we now stand on 

 Ewyas Harold Common we can see nothing except that formation. The higher 

 portions, though not quite the highest, are seen in the Black Mountain on the 

 west and the Skyrrid on the south, while to the south-east and cast, we see the 

 lower ranges of the Graig, Garway, and Saddlehow. In the few remarks I am 

 about to make I shall confine myself to the geology of the district we visit to-day. 

 We are placed on one of a aeries of hills which run somewhat parallel to the Black 

 Mountain. You observe that the sides of the hill are steep ; the cause of this is 

 evidently the power of resisting denudation of that great bed of Cornstone which, 

 as you have just seen, is close to the surface, and produces the flatness of the 

 plateau over which we have just passed. We shall presently see that Ewyas 

 Harold Castle stood on a similar plateau at the end of the King-street hilL 



Now with regard to defining the position of the beds which we see exposed 

 here, I may remark that in this formation, as displayed in this district, we are 

 placed under great difficulties, both from the paucity of organic remains and the 

 similarity of the rocks, compared, for instance, with the Silurian. The divisions 

 of the Old Red Sandstone are consequently very vague. Usually it is divided 

 into an upper or Conglomerate, a middle or Brownstone series, and a lower or 

 Cornstone series, and to those is sometimes added a fourth division, the Ledbury 

 shales. These, however, with the exception perhaps of the last, are general and 

 indefinite divisions, and it appears to me that a great step would be gained if we 

 could establish one or more zones, and break up this great mass into more definite 

 divisions. I am not now in a position to propose such divisions, but merely to make 

 some suggestions which future observations may show to be practicable or not. 

 The Cornstones are usually spoken of collectively and indefinitely, without any 

 distinction as to essential differences. Last year I pointed out that there were 

 two great classes of Cornstone, which I called the Concretionary and the Conglo- 

 merate, the former quite unfossiliferous as far as I had observed, the latter cften 

 containing fossils. Further observation has strengthened my belief as to the 

 essential difference of those deposits. If we look at the geological map, we see 

 no series of the blue lines indicating Cornstone along the sides of the Black 



