Three strata of toadstone had been found, and the limestone under the third was as far as miners had reached. The map project describes the "shallow tropical sea surrounded by coral reefs" in which the limestones were laid down and how "subterranean volcanoes erupted spasmodically through the sea floor, covering the limestones with ash and lava" which formed the toadstone.
372,200,000 to 358,900 years ago Famennian age of the separated by about 10 million years.
About 375 million years ago, towards the end of a time interval called the Givetian.
It mentions the following periods to indicate how long ago coal was formed: Carboniferous followed by 359,200,000 - 326,400,000 years ago Dinantian series or epoch from the Lower Carboniferous system in Europe 326,400,000 to 313,400,000 years ago Namurian stage in the regional stratigraphy of northwest Europe are found - Silicious Grit, providing stone for building and millstones - Shale - then lime-stone and toadstone alternately.
The veins of metallic ores appeared in the limestone.
It is suggested that analysis of sedimentary pyrite from the Belingwe sedimentary basin in Zimbabwe may provide evidence for bacterial reduction at this date.
2,500,000,000 to 542,000,000 years ago The Proterozoic Eon: the most recent part of the Precambrian Supereon.
By carboniferous [carbon bearing] soils, Richard Kirwan in 1799 meant the "various sorts of earth or stone among or under which coal is usually found".
William Daniel Conybeare and William Phillips (1822, page vii) proposed to consider all rocks in an ascending order with a group including "not only the great coal-deposit itself, but those of the limestone and sandstone also on which it reposes" as the "medial" [middle] order.
4,540,000,000 (4.54 billion) years ago Formation of planet Earth - Usher's date was ).
Archeozoic: end of Azoic to 2,500,000,000 years ago: The era of the earliest living beings on earth.
This was not adopted, but his division into Mississippian, for the 's "Story of a piece of coal" focuses on coal formation, but includes a section on the carboniferous limestone.