There is,
therefore, in all likelihood, a general cause for such a coincidence.
Nevertheless, we must not forget that there are dense masses of red and
variegated sandstones and clays, thousands of feet in thickness, and of vast
horizontal extent, wholly devoid of saliferous or gypseous matter. There are
also deposits of gypsum and of common salt, as in the blue-clay formation of
Sicily, without any accompanying red sandstone or red clay.
These red deposits may be accounted for by the decomposition of gneiss and mica
schist, which in the eastern Grampians of Scotland has produced a mass of
detritus of precisely the same colour as the Old Red Sandstone.
It is a general fact, and one not yet accounted for, that scarcely any fossil
remains are ever preserved in stratified rocks in which this oxide of iron
abounds; and when we find fossils in the New or Old Red Sandstone in England, it
is in the grey, and usually calcareous beds, that they occur. The saline or
gypseous interstratified beds may have been produced by submarine gaseous
emanations, or hot mineral springs, which often continue to flow in the same
spots for ages.
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