and the Palcsozoic System of England. 485 



accuracy of these sections I have no doubt; though I may 

 remark, that the cleavage planes of Noedd Grug are not given in 

 the section of the Survey quite correctly, for they deviate with 

 the flexures of the beds j so that in one place, where the beds are 

 highly inclined, the cleavage planes (if I may trust my remem- 

 brance of the phsenomena after a lapse of twenty years) become 

 nearly horizontal. It was in the hope of solving this peculiarity 

 of structure that in 1834 I accompanied my friend Sir R. I. 

 Murchison over Noedd Grug ; and it was the only instance in 

 this part of Wales in which I went with him towards the beds 

 which he then regarded as the geographical boundary of his 

 system. He placed the boundary a little beyond the northern 

 limit of the ridge. 



I lament that an attack of indisposition (the only interruption 

 during our short tour) prevented me from accompanying my 

 friend Prof. ^PCoy over the ridge of Noedd Grug ; and he was 

 so entirely unacquainted with the fossil localities that he did 

 not wish to make the traverse by himself. Our observations were 

 therefore confined to the south end of the ridge (Castell Craig 

 Gwyddon), and to the shale beds immediately overlying it. 



1st. Respecting the Old Red Sandstone, and the greater part 

 of the great Silurian group (Wenlock, &c.}, there can be no dis- 

 pute. 2nd. As to the stage of shale and earthy slates (No. 4 

 of the figure) which come next in order, we sought diligently for 

 its fossils, but we did not find so much as one ; and from its 

 mineralogical type, we did not see how it could either be classed 

 with, or separated from, the Wenlock shale. 3rd. The hard, and 

 nearly vertical, beds of gray sandstone which rise from beneath 

 the shale are too well known to need detailed description. In 

 places they become of coarse structure, but they do not, so far 

 as I know, ever pass into a coarse conglomerate, like that of 

 Dol Fan or Bwlch Trebennau. 



The upper beds of the great precipice contain (as will be shown) 

 a fine May Hill series of fossils. Hence it seems natural to con- 

 clude, that the shales immediately overlying these beds are a true 

 part of the Wenlock shale ; an opinion I should hold, unless the 

 contrary could be proved by fossil evidence, which probably will 

 not be done. Whether the May Hill group of fossils extends 

 through the whole of the contorted sandstone group of Noedd 

 Grug, or is confined to its upper portion, we were unfortunately 

 unable to determine, for the reason above given. But I think I 

 may affirm, from the remembrance of bygone years, that to the 

 north of Noedd Grug, and near Cefn-y-garreg, true Cambrian 

 fossils are met with in abundance. Not, however, to detain the 

 reader with conjectures, I subjoin the list of fossils collected at 

 Castell Craig Gwyddon. - *^ 



