SECTION OF THE CARADOC SANDSTONE (BANKS OF THE ONNY). 217 



I will first describe a natural section on the banks of the river Onny, commencing 

 near Wistanstow, where the strata rise from beneath the Wenlock shale, and termi- 

 nating with the lowest beds of the formation at Horderly Gate. Although a clear order 

 of succession in the upper masses is here exhibited, this section does not fully develop 

 all the subordinate parts of this formation ; and therefore each subdivision displayed 

 on the banks of the river, will afterwards be traced on its strike, to show the great ex- 

 pansion of some beds, in their course to the north-east, or in those hills which form 

 the south-eastern flank of the Caer Caradoc. 



Transverse Section on the Banks of the Onny. — i. Thinly laminated, sandy shale, only slightly micaceous in the upper part, 

 but more so in the inferior, and weathering to a yellow colour. It contains thin courses (one to four inches) of sandstone 

 charged with fragments of shells, and streaked with thin layers of whitish pipeclay, and towards the lower part many thin 

 bands of impure sandy limestone. The latter may be detected in the bed of the Onny, and when first quarried, the layers, 

 four or five inches thick, are of a dull, dark grey, or bluish colour, and break into lozenge shapes. 



Some of the calcareous bands in this subdivision expand in their progress to the 

 north-east. For example, at the Hollies, to the east of Hope Bowdler, there are several 

 courses eight to ten inches thick, which have been extracted and burnt for lime, (g of 

 wood-cut, p. 196.) 



The fossils characteristic of the upper zone of the Caradoc formation are figured in PI. 19. 

 Among them are Productus sericeus, f. l.j JBellerophon bilobatus and B. acutus, f. 13 and 14.; 

 Littorina striatella, f. 12. ; Orthis alternata, O. callactis, (b) Dalman, figs. 5, 6, and O. canalis, 

 PI. 20. f. 8.; Pentamerus Icevis, and P. oblongus, f. 9 and 10. We here lose all traces of the 

 trilobites common to the Upper Silurian rocks (PL 7-)> and in place of them we meet with other 

 forms, including the Trinucleus l , Llhwydd., a genus never observed in the Upper, yet abounding 

 in the Lower Silurian rocks, particularly T. Caractaci, Nob., PI. 23. f. 1., and an undescribed large 

 species of Asaphus, which I have named A. Powisii. (See PI. 23. f. 9 and 10.) 



Impure limestone is also very generally found in the upper beds of the Caradoc sand- 

 stones, in distant parts of Herefordshire, as on the western flank of the Malvern Hills, 

 where besides some of the above-mentioned fossils, it contains some Orthoceratites and 

 many fragments of Crinoidea. It forms also the outer coat of the central dome of the 

 Caradoc sandstone in the valley of elevation at Woolhope, hereafter to be described. 



These upper beds, on the Onny, dip 20° S.E. beneath the Wenlock shale, containing 

 the Asaphus longicaudatus , (PL 14. f. 11, 12, 13, 14.) whilst the lower strata graduate 

 downwards into sandy flagstones. They are placed at the top of the Caradoc forma- 

 tion, not only by their stratigraphical position, but also by their mineral structure and 



1 Fragments and imperfect specimens only of these Trilobites having been published, I was about to name 

 this genus Tretaspis from Tprjrij aairls, a shield perforated or deeply sculptured on its margin, for such is the 

 leading generic distinction; when considering that an unquestionable species of this genus was long ago figured 

 by Llhwydd (Lythophyl. Brit. Ichnogr. 1699, p. 97. t. 23,) as Trinucleus fimbriatus, I have in obedience to the 

 practice of the best zoologists retained the original name. The American author Green, to whose work I shall 

 have occasion to refer in the sequel, (see chapters on organic remains,) has recently proposed that this genus 

 be called Cryptolithus , but this term does not explain any peculiarity of organization, and offers no inducement 

 to relinquish the name of the old English naturalist. 



