The mineral had, however, been earlier known as a blue powdery substance, called "blue ironearth," met with in peat-bogs, in bog iron-ore, or with fossil bones and shells.
The wood, of unknown age, found submerged in peat-bogs, and of a black hue, is largely used in decorative art under the name of "bog-oak."
Warming included plants of peat-bogs among his hydrophytes.
The soil is mostly sand, clay (brick-clay and potter's-clay are not uncommon), and peat-bogs,with a few patches of "black earth."
In former ages the tree covered a large portion of the more northern part of the island, as well as of Ireland; the numerous trunks found everywhere in the mosses and peat-bogs of the northern counties of England attest its abundance there in prehistoric times; and in the remoter post-Glacial epoch its range was probably vastly more extended.