D. C. Davies—The Millstone Grit of North Wales. 125 



make their appearance : Calamito stems, for example, lying em- 

 bedded amidst slioals of Productus aemireliculaluH, var. Martini. 



lu his " Geoh)gy of Yorkshire," Professor Pliillips enumerates 

 about 16 species of fossils obtained from tbo Millstone Grit of that 

 county, but these were derived from the limestones, ironstone- 

 nodules, and shales. The distinguishing feature of the Millstone 

 Grit we are considering, is, that the fossils are obtained almost 

 exclusively from its Sandstones, occurring in a beautifully perfect 

 state of preservation in even coarse and pebbly grits, for example, 

 in the Forest quarry, at Cyrnybwch, we find the sharp striae and 

 ridges of Streptorliynclius crenistria uninjured in the coarse sandstone, 

 and lying in close proximity to pebbles. In this respect the matrix 

 in which the fossils are imbedded differs from that in which the 

 fossils described by Lieutenant Austin, from the Bristol district, are 

 found. These are set in a matrix of calcareous sandstone, like that 

 we find at the base and in the centre of the North Wales group. 

 The fossils that occur in the beds of the North of England are 

 interesting, as showing a similar fauna to that of North Wales, 

 extending similarly upwards to the Coal Measures ; and, as we 

 cannot suppose that the fauna disappeared and reappeared with each 

 change from calcareous to sandy conditions, we must conclude that 

 there are nests of fossils somewhere, in the intervening sandstones, 

 which have yet to be found. 



There is an entire absence of seams of coal in the Millstone Grit of 

 North Wales, and in this respect also it differs from that of the North 

 of England. The presence of land-plants, however, renders it possible 

 that, somewhere or other, there may yet be found the remains of an 

 early Carboniferous flora in carbonaceous shales, or thin seams of 

 coal. There is a line representing one of the latter on the geological 

 map for the Owestry district, but this is an error. The coal on its 

 course belongs to the true Coal Measures, and is not interstratified 

 with the Grit, the portion between Mynyd Mj'^fyr and Carneddau 

 being a partially denuded outlier of the main field. 



I have throughout this paper assumed that the rocks I have been 

 describing are really Millstone Grit, but I am conscious that the 

 correctness of this assumption has been questioned, indeed I think 

 that I was myself the first to do so, for, in 1861, I wrote,^ " The 

 Yoredale series, which in Yorkshire presents an alternation of beds 

 of shale, limestone, sandstone, and coal, is not represented in North 

 Wales, unless we regard the uppermost beds of limestone and shale, 

 and the lowest fossiliferous layers of Millstone Grit in our neigh- 

 bourhood as occupying the same horizon, viz., lying between the 

 limestone proper and the coarse and unfossiliferous Grits.^ Mr. 

 Green, of the Geological Survey, in a contribution to the Geol. Mag., 

 1867, Vol. lY., p. 11, suggested pretty much the same division; 

 and Mr. John Aitken, of Bacup, who has well studied the Grits of 

 his own neighbourhood, thus wrote to me, after some excursions we 



1 Proceedings of the Owestry Field Club. 



2 At this date my knowledge of the extent to which the fossils extend upwards in 

 the Grit was limited. 



