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Everybody at all acquainted with the Old Red Sandstone must often have been 

 struck with its prodigious number of nodules, containing in nine cases out of ten a 

 nucleus of organic matter, with spherales of black or colourless blotches. In accounting 

 for them Sir C. Lyell gives the following beautiful story : — " An earthern pitcher contain- 

 ing sulphate of iron had been suffered to remain undisturbed for twelve months. Some 

 luckless mice had meanwhile fallen into it and been drowned. When it came to be 

 examined, an oily scum and a yeUow sulphurous powder, mixed with hairs, were seen 

 floating on the top, and the bones of the mice discovered at the bottom Over the 

 decaying bodies the mineral components of the fluid had been separated and precipi- 

 tated in a dark-coloured sediment, consisting of grains of pyrites and sulphur of copperas 

 in its green and crystalline form, and of black oxide of iron. The animal and mineral 

 matters had acted on eacli other, and the metallic sulphate, deprived of its oxygen in the 

 process, had cast down its ingredients." In like manner, we are told, the putrifying 

 bodies of the fish of the Old Red were covered with a deposit of lime, with which 

 the water was charged, and hence the nodules enclosing them. The form of the nodule 

 almost invariably agrees with that of the ichthyolite within. It is a cofHn in the 

 ancient Egyptian style. Was the ichthyolite twisted half round in the contorted atti- 

 tude of violent death ? the nodule had also its twist. Did it retain its natural posture ? 

 the nodule presents the corresponding spindle form. Was it broken up and the outline 

 destroyed ? the nodule is flattened and shapeless. In almost every instance the form of 

 the organism seems to have regulated that^f the stone. 



The next fact to be noticed is still more important in this immediate neighbourhood. 

 I shall give it in the words of Hugh Miller. "A very dilferent chemical effect of 

 organic matter may be seen in the darker coloured arenaceous deposits of the formation, 

 and occasionally in its stratified clays. In a print-work, the whole web is frequently 

 thrown Into the vat and dyed of one colour ,■ but there afterwards comes a discharging 

 process. Some chemical mixture is dropped on the fabric ; the dye disappears wherever 

 the mixture touches, and in leaves, in sprigs, and patches the cloth assumes its original 

 white. Now, the coloured deposits of the Old Ked have in like manner been subjected 

 to a discharging process. The dye has disappeared in oblong or circular patches of 

 various sizes, from one eighth of an inch to a foot in diameter ; the original white has 

 taken its place ; and so thickly are these speckles grouped in some of the darker tinted 

 beds, that the surfaces, where washed by the sea, present the appearance of sheets of 

 calico. The discharging agent was organic matter. The uncoloured patches are no 

 mere surface films, for when eut at right angles their depth is found to correspond 

 with their breadth. It is well for the young geologist carefully to mark such appearances, 

 to trace them through the various instances in which the organism may be recognised 

 and identified, to those in which its least vestiges have disappeared. They are the 

 hatchments of the geological world, and indicate that life once existed when all other 

 legible record of it has long since perished." All over this district these are specially 

 abundant, as shown by almost every stone wall in Breconshire. Perhaps one half the 

 pebbles you look at are colourless in the middle. 



Besides, however, the great mass on which we now stand, there are very important 

 outliers, like islets of Old Red in an ocean of gray, especially interesting to geologists. 

 See, for example, the Forest of Clun, near Newtown, covering about ten miles square, 

 composed of the lower group of the old red, and having the Silurian underneath. 

 See another, about five square miles, between Presteign and Knighton, and a third, 

 still smaller, on the S.W. of Presteign, called Nash Scar Ridge. It is sufficient to state 

 that these have been separated from the main by elevatory forces, which pushed in 

 igneous rocks and caused gieat denudation in the overlying deposits. Wherever they 



