261 



upper division. A scale of Holoptychius nobilissimus, found by Sir Roderick 

 Murchison on the Daren, near Crickhowell, prior to the publication of the " Silurian 

 System," was the only indication we had 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 and 

 Professor Melville, of the remains of Holoptychius.* I hope, therefore, our 

 indefatigable Ludlow members will pursue their researches further in this direc- 

 tion, and that Dr. Bevan and our Abergavenny members will \ie with them in 

 the endeavour to trace the limits of the uppermost beds of Old Red.f I cannot 

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

 Roderick Murchison in the appendix to the last edition of Siluria, p. 55<3) that 

 the Old Red Sandstone is necessarily a red rock. He says, " the true base in 

 Shropshire and Herefordshire of the Old Red Sandstone, properly so-called, is, 

 I repeat, seen to be a red rock, containing Cephalaspis and Pteraspis, and gradually 

 passing down into the grey Ludlow rock." Now, although this is generally the 

 case in the Old Red 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 red soil, arising from the denudation of the 

 Black mountains and other elevated masses of the Old Red, but the rocks beneath, 

 including those which 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 fossils as the 

 indicators of the stratigraphical position of the rocks in which they are found ; 

 but he may view them with the eyes of a naturalist, and compare them with 

 animals which now e.xist, tracing the affinity of extinct to existing species ; he 

 will thus note their differences, learn their habits, and form a notion of the con- 

 ditions under which these animals of the past existed— he will marvel that the 

 worm should have left its track and burrows, the ebbing tide its ripple, and the 

 raindrop its record on the surface of the rocks ; he will observe the Trilobite, 

 one of the earliest crustaceans, attain its greatest development in the Silurian 

 period, and gradually become extinct in the Carboniferous rocks— he will be 

 struck with its varied form, elaborate stiucture, and the countless facets of its 

 eye— he will compare the Orthoceratites and the numerous Cephalopods with 

 their allies, the extinct Ammonites, and the Nautilus of the present seas ; and 

 will see in each species the same chambered structure and the same provision 

 for floating on the surface of the water, although the forms are so various and 

 unlike ; he will admire the numerous and varied series of Corals and Crinoids in 

 the Limestones, the elegant Star-fishes and numberless MoUusca of the Silurian 

 seas, and when these last are gradually dying away, he will see the Pterygoti and 

 Eur\-pterida5, the largest of Crustaceans, for a brief time the principal occupants 



* Symonds' " Old Red Sandstones of Herefordshire," ubi supra. 



t Morris and Roberts "on the Yellow Sai.dstone and Mountain Limestone of Oreton .ind 

 Farlow. ' Quarterly Journal. Geologic.-il Society, vol. i8, p. 94. 



