58 A CHAPTER IN THE PHYSICAL GEOGRAPHY OF THE PAST. 
vegetable mass. Doubtless some such cause as this produced the 
extraordinary purity of some of our coal seams. 
In picturing to ourselves the appearance of those huge, swampy 
flats of the Coal Period, which covered hundreds of thousands of 
square miles, we must not imagine a forest growth like that of the 
present day. The predominating forms, and those whose remains 
had most to do with coal-forming were Crypfogams, and consisted 
of trees related to our Lycopods or Club Mosses, and to our 
Equiseta or Horse Tails. These acquired proportions which were 
truly gigantic as compared with their lowly and degenerated 
modern representatives. The ferns were mostly of the herbaceous 
kinds, but some large Tree Ferns also existed, far outstripping in 
height the noble Tree Ferns of our tropical islands. We look 
in vain for the higher orders of the flowering plants, for the 
Phanerogams were only represented by their lowest order the 
Gymnosperms, which included some Conifers, and a few Cycads. 
These dense and tangled brakes were not without animal life, for 
we have found in the Coal Measures remains of scorpions, spiders, 
cockroaches and crickets. The Coleoptera were also represented, 
but, as far as we know at present, the Lepidoptera did not yet 
exist; nor is this to be wondered at when we consider the entire 
absence of the higher flowering plants. In the waters were 
numerous fish, but the only known air-breathing Vertebrates were 
Amphibia, of which the Labyrinthodonts, huge frog-like animals, 
were the chief. These are known to us principally by the curious 
hand-like footmarks which they left upon the mud. 
The remains of these great sub-tropical forests must have formed 
originally very thick masses of peat, probably ten or twenty times 
thicker than the coal seams they were destined to become. This 
peat consisted, for the most part, of the decomposed cellular tissue 
of plants which grew upon the spot; and, within the Jast few 
years, we have had a curious piece of evidence to show that the 
initial decomposition of the tissue was effected, not by the mere 
chemical action of air and moisture, but by the agency of those 
minute living organisms which we now recognise as playing such 
an important part in all putrefactive and fermentative change. 
Oe ey ee ry EEE 
