ORGANIC REMAINS OF THE TILESTONE FORMATION. 



183 



house called Horeb Chapel, have their dip increased to sixty-five and seventy degrees, 

 and are of greenish and grey colours, but these are again underlaid by other beds of a 

 reddish colour, so that the whole of the tilestones are clearly subordinate to the Old 

 Red System. The greenish beds split to an average thickness of three or four inches, 

 are much jointed, and have frequently an imperfect slaty cleavage transverse to the 

 bedding ; they are highly charged with mica, both disseminated and in laminse. The 

 joints are for the most part vertical, and their faces are frequently coated with crystals 

 of white quartz. 



Organic remains are abundant, and indicate clearly the lines of deposit, whilst the 

 transverse cleavage and the faces of the joints are strongly marked by sharp planes 

 cutting obliquely through the fossil layers. The fossils consist of unpublished species 

 of the following genera : Area, Avicula, Bellerophon, Cucullcsa, Lingula, Orthoceras, Te- 

 rebratula, Turbo, Turritella, Trochus, with the Tentaculites scalaris (Schlotheim) . 



This assemblage furnishes convincing proofs that certain genera of mollusks, such as 

 Area, Cucullcea, Turbo, Trochus, &c, which have hitherto been supposed to be confined 

 to the younger or tertiary and secondary deposits, have co-existed with the genera Or- 

 thoceras, Terebratula, Bellerophon, which peculiarly characterize the older strata. (See 

 PI. 3. and subsequent description of these fossils.) 



Tilestone Group, east side of Herefordshire. — As the Old Red Sandstone lies in a vast 

 trough bounded by the Silurian System both on its eastern and western flanks, we ought 

 to find its lower member, or tilestones, forming the western fringe of the Malvern Hills. 

 Owing, however, to high inclination, the accumulation of detritus, and other results of 

 disturbance, these beds are rarely well displayed for any distance along the eastern 

 frontier of the Herefordshire basin. They are, however, clearly laid bare in a natural 

 transverse section at Brockhill Knell between Mathon and Ledbury, where thin bands 

 of yellowish green, micaceous flagstone, one and two inches thick, are subordinate to 

 red, green and purple marls, the whole dipping away to the west and overlying the 

 grey Ludlow rocks at an angle of forty-five degrees. (See PI. 36. fig. 7.) Hard and 

 thin flaggy rocks belonging to this group are also seen at the north-eastern suburb of 

 Ledbury, dipping fifty -five degrees west-north-west, but the flanks of the ledges of older 

 rocks near that town are encumbered with so much stiff red clay and detritus that the 

 exact junction beds can rarely be distinguished. (PI. 37. fig. 8.) The same causes of 

 obscuration, apply to the line of junction between the Old Red Sandstone and the Silu- 

 rian rocks of the May Hill range. In some valleys of elevation, however, the upper 

 surfaces of the grey-coloured Silurian Rocks, which are thrown up in their interior, ex- 

 hibit on their external faces clear examples of passage into the bottom beds of the Old 

 Red Sandstone. This is well seen on the eastern slopes of the Clytha Hills, two or 

 three miles east of Ragland, and will be further alluded to in the sequel. 



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