Some coal balls from the US vary in age from the later end of the Stephanian ( roughly 304 to 299 mya ).
32.
For instance, the very first sentence in the very first book in this search says that coal balls are found in the Permian.
33.
Their unique preservation of Carboniferous plants makes them valuable to scientists, who cut and peel the coal balls to research the geological past.
34.
"' Coal balls "', despite their name, are calcium-rich masses of geological past of the Earth.
35.
During Stopes's time at Manchester, she studied coal and coal balls and researched the collection of Glossopteris ( Permian seed ferns ).
36.
Mixed coal balls are further divided into heterogeneous, where the plant and animal material was distinctly separated; and homogeneous, lacking that separation.
37.
Since then, coal balls have been discovered in other countries and they have led to the discovery of over 300 species and 130 genera.
38.
His scientific research, besides his early original work on fossil plants and coal balls, was chiefly concerned with vertebrate palaeontology, especially fossil reptiles.
39.
Coal balls often preserve a remarkable record of the microscopic tissue structure of Carboniferous swamp and mire plants, which would otherwise have been completely destroyed.
40.
The oldest known coal balls date from the Namurian stage of the Carboniferous; they were found in Germany and on the territory of former Czechoslovakia.
