MONIAN SYSTEM OF EOCKS. 465 



felsitic conglomerate with large pebbles. The exposure of these 

 rocks is not a large one. They form a superficial patch for about 

 half a mile. At their northern end the schistose masses reappear 

 ■within a few yards of the uppermost conglomerate, so that the 

 junction can scarcely be anything but a fault. At the southern end, 

 however, described by Prof. Bonney, the lowest blue grit may now 

 be seen to have its base continuous with the surface of the older 

 rock from which it has been taken off up to a joint face. The 

 junction here, therefore, is not a fault, but the grit lies on the surface 

 of the other rock, and is as much unconformable as it can be, seeing 

 there is no definite bedding in the schistose mass. These schists 

 are, therefore, definitely Pre-Cambrian. 



Similar and confirmatory evidence can now be brought forward 

 from the neighbourhood of Eed-Wharf Bay. On the east side of 

 this bay may be seen a " feature '' which runs, on the Ordnance map, 

 from AVern to Llaniestyn. On the south-west of this line, and 

 forming the escarpment, we find the schistose rocks, with the orien- 

 tation of their folia striking directly at the line. On the north- 

 east, and generally at a lower level, forming another feature running 

 thence towards Llandona, we find the same grits, hiilleflintas, and 

 conglomerates as at Beaumaris, with their bedding parallel, or 

 nearly so, to the escarpment. Eor more perfect satisfaction I have 

 examined microscopically the rocks from these two localities, and 

 compared them with those of Bangor, and they are found to agree 

 in character. But there is really no need for this ; no one could 

 mistake their common character, even in the field. 



To my own mind, however, the most perfect proof of unconformity 

 is derived, not from isolated sections, but from the same basal rocks 

 lying in different localities upon different members of the older series, 

 without the latter in any way dying out. This proof can only be 

 afforded alter obtaining an acquaintance with the sequence of the 

 older rocks ; when this has been done, it is seen that the northern 

 patch lies on the older, and the southern on the younger portion of 

 the series. I cannot conceive a more perfect stratigraphical proof of 

 the point in question. 



Yet it appears to me that it is the observation of a portion of these 

 facts that led Sir A. Bamsay to exactly the opposite conclusion. 

 He states that the "grounds on which the larger part of Anglesey 

 is considered to consist of Cambrian rocks " are as follows : — " If 

 we prolong the strike [of the Bangor rocks] and of the overlying 

 Silurian beds from Bangor, under the Lavan Sands to Beaumaris, 

 and from thence to Glan-y-ffynon at the east point of Eed-Wharf 

 Bay [exactly the two localities above described], we find an associa- 

 tion similar to that of Bangor, black slates resting on green, grey, 

 and purple schists and grits, which, however much foliated and 

 contorted, still bear a strong resemblance to the Cambrian rocks 

 of Bangor." Hence it is evident that Sir A. Eamsay has seen these 

 Cambrian rocks in Anglesey, has recognized their resemblance to 

 those of Bangor, but has conceived that there was a passage from 

 these rocJcs into the schists, instead of an unconformity between 



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