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ON THE "OLD EED SANDSTONE," AS SEEN FROM 



THE SUGAE-LOAF MOUNTAIN, IN THE COUNTY 



OF MONMOUTH, ON THE 10th JULY, 1885. 



By G. H. Piper, F.G.S. 



I HAVE been asked by our President to address you on the features of tlie dis- 

 trict ; and, inasmuch as we are on the top of a mountain of Old Red Sandstone, 

 and all that is near enough to us to be distinguishable is of the same geological 

 structure, the natural consequence is that I must discourse upon that very ancient 

 and highly interesting formation. It may be taken for granted that you all 

 know that the Coal Measures are a sort of middle formation, lying beneath the 

 New Red Sandstone and above the Old Red, and although these tenns are too 

 general for the purposes of science, they are still sufficiently distinctive, and have 

 the advantage of beinif ea.sily remembered. The Old Red Sandstone embraces the 

 whole series of strata which lie between the Silurian system laelow the Old Red, 

 and the Carboniferous system above it. The Old Red Sandstone, or Devonian, 

 for the latter term is now generally employed as synonymous with the earlier and 

 more descriptive one, is one of the most remarkable and clearly defined on the 

 surface of the globe. Characterised on its lower margin by strata containing the 

 remains of cephalaspidean fishes, which have been found in considerable numbers 

 in the lowest beds of the Old Red at Ledbury, and in the passage beds there 

 which form a line of separation between it and the underlj'ing Silurian, and 

 defined, on its upper margin, by the rarity of that vegetation which enters so 

 profusely into the composition of the carboniferous rocks, there can, in general, be 

 no difficulty in determining the limits of the Old Red formation. Hugh Miller 

 asserted in his admirably written treatise on the Old Red Sandstone, that no trace 

 of the curious ichthyolite, Cephalaspis is found among the fossils of the lower Old 

 Red Sandstone. He says : "Neither in England nor in Scotland is it to be found 

 in the Tilestone formation, or its equivalent. It is exclusively a medal of the 

 Middle Empire." Subsequent researches have shown this statement to be in- 

 correct. My collection of Cephalaspides was obtained almost entirely from the 

 base of the Old Red, and amongst them I have bodies of the very rare Auchena- 

 spis Egertonii — head plates of this curious little fish are seldom found, and I 

 believe no body, or fragment of a body, is to be seen outside of my museum. The 

 Old Red system is manifestly arenaceous, the great bulk of it is made up of sand- 

 stones and conglomerates with subordinate strata of shales and concretionary 

 limestones. This statement is capable of immediate proof, for the fine dust upon 

 which I now stand is part of the mountain disintegrated by the slow action of 

 frosts, rains, and other atmospheric influences, and although the particles are so 

 minute as to be severally almost imperceptible, yet you will find by the aid of a 

 microscope that most of these insignificant atoms are blocks of pure quartz. 



