Another and very different chemical effect of organic matter may be remarked in the darker colored arenaceous deposits of the formation, and occasionally in the stratified clays and nodules of the ichthyolite bed. In a print-work, the whole web is frequently thrown into the vat and dyed of one color; 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, and sprigs, and patches, according to the printer's pattern, the cloth assumes its original white. Now the colored deposits of the Old Red Sandstone have, in like manner, been subjected to a discharging process. The dye has disappeared in oblong or circular patches of various sizes, from the 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 uncolored patches are no mere surface films, for, when cut at right angles, their depth is found to correspond with their breadth, the circle is a sphere, the ellipsis forms the section of an egg-shaped body, and in the centre of each we generally find traces of the organism in whose decay it originated. I have repeatedly found single scales, in the ichthyolite beds, surrounded by uncolored spheres about the size of musket bullets. 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 recognized and identified, to those in which its last vestiges have disappeared. They are the hatchments of the geological world, and indicate that life once existed where all other record of it has perished.[BC] [Footnote BC: Some of the clay-slates of the primary formations abound in these circular, uncolored patches, bearing in their centres, like the patches of the Old Red Sandstone, half obliterated nuclei of black. Were they, too, once fossiliferous? and do these blank erasures remain to testify to the fact? I find the organic origin of the patches in the Old Red Sandstone remarked by Professor Fleming as early as the year 1830, and the remark reiterated by Dr. Anderson, of Newburgh, in nearly the same words, but with no acknowledgment, ten years later. The following is the minute and singularly faithful description of the Professor:--