234 THE OLD RED SANDSTONE. 
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 subject- 
ed 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 cal- 
ico. The discharging agent was organic matter; the ‘uncol- 
ored 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, sur- 
rounded by uncolored spheres about the size of musket bul- 
lets. It is well for the young geologist carefully to mark 
such appearances—to trace them through the various in- 
stances in which the organism may be recognized and iden- 
tified, to those in which its last vestiges have disappeared. 
They are the hatchments of the geological world, and indi- 
cate that life once existed where all other record of it has 
perished.* 
* 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 
so testify to the fact? I find the organic origin of the patches in the 
