The Rev. Prof. Blake — Base of the Sedimentary Series. 313 



occurs a fossiliferous band containing Orthides, of which the most 

 characteristic is Orthis Bayleana. Prof. Hughes's own solution of 

 the difficulty thus arising appears to be that this is here a continuous 

 upward sequence from the Areuig slates which occur in the centre of 

 the island. This ignores the great fault by which the two are 

 separated, according to every other observer. . The only other 

 solutions at present suggested are either that the fossiliferous 

 bands are faulted in, or that the fossils are really characteristic 

 of the Precambrian series. Against the former solution is the 

 fact that the containing rocks are just like the rest for some 

 distance north and south, and that no fault which should have 

 the required effect can be seen, even by careful observation directed 

 to this very object, in the adjacent clear coast sections. The only 

 recognized faults in the neighbourhood let down narrow troughs 

 of dark shales with Llandeilo Graptolites, which are therefore 

 younger than the surrounding mass, and not older as they should 

 be if the latter were of Bala age. Still, if the third solution be 

 not accepted, the next most probable one would be the existence 

 of some disturbance not as yet properly understood. The third 

 solution, that the fossils found are characteristic of Precambrian 

 rocks, seems too startling at first to be entertained at all — Ortltis 

 in Precambrians ! Nevertheless there is something to be said on 

 this point. The principal and in fact only definitely recognizable 

 species is a very well marked one, and in spite of the abundant 

 fauna of North Wales it has never been seen there, in any other 

 locality. I have compared it with the type which comes from near 

 Wexford, and there cannot be the slightest doubt that it is the same 

 species. Orthis Bayleana. I have been to Wexford to try to learn 

 its true position. But I never saw such a jumble of rocks as are 

 there exposed ; it is perfectly hopeless to learn anything of their 

 position. But two things I learned, first, that this species nowhere 

 occurs in the true slaty Ordovicians, which are not man}' miles away, 

 and that the matrix is quite different. It is said to be associated 

 with recognizable Trilobites, but these again occur in an entirely 

 different matrix. 



In answer to the second question — whether these rocks form one 

 system or several — Dr. Hicks replies by implication that there are 

 three, since in certain spots he thinks to recognize his Dimetian, 

 Arvonian, and Pebidian. By the proof, however, which I have 

 abundantly given, and which is for the most part now accepted, that 

 the granite referred to the Dimetian is an intrusive rock, these 

 reduce to two ; but as no detailed observations bearing on the 

 question have been published by this author, there is no occasion to 

 discuss whether the remaining divisions represent real groups. 



But Dr. Callaway's description is directly to this point. According 

 to him there are two distinct groups, the " gneissic " and the " slaty." 

 The evidence adduced in support of this is threefold. 1. That one 

 of the " slaty " rocks contains fragments of a " gneissic " rock. 2. 

 That at one spot a rock referred to the slaty group contains frag- 

 ments of a granite referred to the gneissic group. 3. That the 



