COAL FIELDS. 259 



_, ■ ,„, . Exogens, common forest and fruit trees. 



Phauerogamia (Flowering plants.) ..Undogens, palms, grasses, grains, etc. 



Gymnosperms, pines, cedars, etc. 



{Club mosses. 

 Ferns. 

 Scouring rushes, etc. 

 Cryptogamia ( Flowerless plants.)...Anogens Mosses, etc. 



Thallogens...{ ^fhens Seaweeds - 



The coals of the Carboniferous age are principally derived from 

 groups of plants that belong near the middle of the series, viz.. from the 

 Acrogens and the Gymnosperms, or, in other words, from the lowest of the 

 flowering and from the highest of the flowerless. The contributions of 

 the Gymnosperms are relatively unimportant and the families of plants 

 from which the coal is almost entirely derived are the lycopods, or club 

 mosses and the ferns. These families were expanded far beyond their 

 present condition of development. They have left such abundant ma- 

 terials for our study in the coal seams and the associated strata that we 

 are able to restore them, with a good degree of confidence as to the faith- 

 fulness of our results. We know their roots, their stems, their bark, their 

 wood, their pith, their leaves, their spores, their fruits. 



It is to the microscope that we owe the final demonstration of the 

 vegetable origin of coal. An addition to our knowledge of its composi- 

 tion, made within the last twenty years, may be stated in this connection. 

 It has been proved by means of thin sections of coal that considerable 

 portions of some seams are made up of the spores and spore cases of lyco- 

 podiaceous plants. Professor Huxley went s"o far, in a paper published 

 in 1870, as to claim that coal of the Carboniferous age is mainly derived 

 from this particular source. While this extreme claim cannot be allowed, 

 it is doubtless true that the spores of the ancient club-mosses, took a large 

 part in the up-building of many seams. 



The spores of modern club-mosses are produced in great abundance. 

 They constitute an article of commerce under the name of tycopotfium, 

 which is found in all drug stores. When it is remembered that the club- 

 mosses of our day are generally less than one foot in height, it. is easy to 

 understand how the gigantic representatives of the order in Carboniferous 

 time, which attained a height of fifty to seventy-five feet, could make so 

 important a contribution to our fossil fuel, as has been claimed for them 

 in the preceding paragraph. The composition of lycopodium is excel- 

 lently adapted to preservation, under the conditions which must have pre- 

 vailed in the coal-forming swamps. 



It seems probable that the division of our coals into coking and open- 

 burning will be found to be based on the particular sources of plant 

 growth from which they are respectively derived. 



Coal seams are generally found combined in great systems, interstra- 

 tified with sand stones, conglomerates, shales, limestones and beds of iron 

 ore, the whole series measuring hundreds and sometimes thousands of 



