English Stratified Rocks below the Old Red Sandstone, fyc. 145 



between the Upper Cambrian and lowest portion of the Silurian 

 system. 

 (2.) Bands of calcareous slate with numerous organic remains ^>f 



the " Caradoc sandstone," surmounted by roofing slate. 

 (3.) Series of flagstones, more or less calcareous, with many Or- 

 thoceratites and two species of Cardiola, &c. ; overlaid by, and 

 associated with, irregular masses of roofing slate with a trans- 

 verse cleavage. 

 (4.) Flagstones and rotten slates, many parts in an imperfect state 

 of induration, and the whole surmounted by the carboniferous 

 limestone. — Of the preceding section the lower part of No. 3 

 is identical with the series of Long Mountain in the Silurian 

 sections of Mr. Murchison ; but No. 4 is mineralogically un- 

 like anything he has described, although it has been found by 

 Mr. Bowman to contain, in its highest portion, some of the 

 fossils of the Upper Ludlow rock. It appears from these details 

 that the Silurian system, although its subdivisions are obscure 

 from the absence of the Wenlock and Ludlow limestones, is 

 very fully developed in North Wales. 

 An examination of the few Snowdonian fossils of the author gives 

 the following results : — 



(1.) Impressions of corals (Turbinolopsis ?) (Cwm Idwal and Moel 



Hebog). 

 (2.) Stems of Encrinites (Cwm Idwal). 



(3.) Orthis pecten, 0. Actonia, 0. flabellulum, 0. canalis (Snow- 

 don and Moel Hebog). 

 He has many fossils from different parts of the Berwyn chain ; 

 and he believes them (as stated in a former abstract) to be nearly 

 all known Silurian species, but they have not yet been carefully 

 examined. He possesses also a good series of fossils from the eastern 

 side of the Berwyns, and from portions of the more northern sec- 

 tions ; but as the whole series is unequivocally Silurian (extending 

 from the Llandeilo flagstone to the Upper Ludlow rocks), he has 

 not thought it at present necessary to trouble the Society with any 

 enumeration of species. 



From a review of these facts he concludes, that in the great sec- 

 tion of North Wales there is no positive zoological distinction in 

 the successive descending groups, however vast in thickness or di- 

 stinct in mineral structure. It is not by the addition of new species, 

 but by the gradual disappearance of the species in the higher groups, 

 that the successive groups are zoologically characterized. Below 

 the Caradoc sandstone there seems to have been very few new types 

 of creation, as far at least as we have learnt from any positive facts 

 in the country here described. This conclusion is nearly in accord- 

 ance with a statement made by the author in a former paper, viz. 



" The difficulty of classification by organic remains increases as 

 we descend, and is at length insurmountable ; for in the lowest 

 stratified groups, independently of metamorphic structure, all traces 

 of fossils gradually vanish ; and the great range of certain species 

 through numerous successive groups, and the very irregular distri- 

 Phil. Mag. S. 3. Vol. 2 1 . No. 1 36. Aug. 1 842. L 



