Murchison's Silurian System. 549 



terval of ninety miles. We may quote the following remarks 

 on one of those sections. 



Between Treeastle and Llandovery, " tilestones are quar- 

 ried, rising at an angle of sixty degrees from beneath the 

 marly and sandy beds of the cornstone group, the lower 

 tilestones graduating downwards into the equivalent of the 

 Ludlow rock. The uppermost beds are of a dark purple 

 colour, the surface being covered by large plates of a grey 

 mica, and here and there certain impressions resembling those 

 in the old red sandstone of Scotland, called * Kelpie's feet.' 



" The lower beds, as worked on the steep acclivity of Horeb 

 chapel, have their dip increased to sixty-five and seventy 

 degrees, and are of greenish and grey colours, but these 

 again are 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 bed- 

 ding ; they are highly charged with mica, both disseminated 

 and in lamina?. 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 consist of unpublished genera, Area Avicula Betterophon, 

 Cuculloa Lingula Orthocera Terebratula Turbo Turrit ella 

 Trachus with the Tentaculites scalaris Scholothein. This 

 assemblage furnishes convincing proofs that certain genera 

 of Molluscs, such as Area Turbo Trachus Cuculloa, &c. 

 which have been supposed to be confined to the young 

 tertiary and secondary deposits, have co-existed with Ortho- 

 cera, Terebratula, Bellerophon." 



Mr. Murchison, in conclusion, estimates the depth of the 

 old red system as it rises from beneath the South Welsh 

 coal basin and over the Silurian rocks of Radnor, to be not 



