13 



of the upper beds, until the discovery at Farlow, in Shropshire, 

 two or three years ago, of a new species of Ptericthys in yellow 

 sandstone, overlaid by the shale of the carboniferous limestone of 

 Clee-hill, and the more recent discovery at the same place, by Mr. 

 LiGHTBODY & Professor Melville, of the remains of Holoptychius.* 

 I hope, therefore, our indefatigable Ludlow members wUl pursue 

 their researches further in this direction, and that Dr. Bevan and 

 our Abergavenny members will vie with them in the endeavour to 

 trace the limits of the uppermost beds of Old Eed. + I cannot help 

 noticing, before I quit this subject, an erroneous notion (adopted by 

 Sir Eoderick Murchison in the appendix to the last edition of 

 SUuria, p. 559) that the Old Bed sandstone is necessarily a red 

 rock. He says, " the true base in Shropshire and Herefordshire of 

 the Old Eed sandstone, properly so called, is, I repeat, seen to be a 

 red rock, containing Cephalaspis and Pteiaspis, and gradually pas- 

 sing down iuto the grey Ludlow rock." Now, although this is 

 generally the case ia the Old Eed of Herefordshire, we know that 

 it is not universally so ; the sandstones in the neighbourhood of 

 Kington, Hay, and other parts of the northern side of the County, 

 are overlaid with a red soU, arising from the denudation of tho 

 Black Mountains and other elevated masses of the Old Eed, but 

 the rocks beneath, including those wliich contain Cephalaspis 

 Lyellii, are generally a grey micaceous sandstone. In this as in 

 other similar cases, we must look to fossil contents rather than to 

 colour and lithological composition as the truest indicator of the age 

 of rocks. 



But the geological observer may not only view the imbedded 

 fossUs as the indicators of the stratigraphical position of the rocks 

 iu which they are found ; but he may view them with the eyes of 

 a naturalist, and compare them with animals which now exist, 



* Symonds' "Old Eed Sandstones of HerefordsMre," ubi supra. 

 + Morris and Roberts "on the Yellow Sandstone and Mountain Limestone 

 of Oreton and Farlow." Quarterly Journal, Geological Society, vol. 18, p. 94. 



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