Again, the late Professor Quekett was one of the first observers who gave a correct description of what I have termed the “saccular” structure of coal; and, rightly perceiving that this structure was something quite different from that of any known plant, he imagined that it proceeded from some extinct vegetable organism which was peculiarly abundant amongst the coal-forming plants.  But this explanation is at once shown to be untenable when the smaller and the larger sacs are proved to be spores or sporangia.

Some, once more, have imagined that coal was of submarine origin; and though the notion is amply and easily refuted by other considerations, it may be worth while to remark, that it is impossible to comprehend how a mass of light and resinous spores should have reached the bottom of the sea, or should have stopped in that position if they had got there.

At the same time, it is proper to remark that I do not presume to suggest that all coal must needs have the same structure; or that there may not be coals in which the proportions of wood and spores, or spore-cases, are very different from those which I have examined.  All I repeat is, that none of the coals which have come under my notice have enabled me to observe such a difference.  But, according to Principal Dawson, who has so sedulously examined the fossil remains of plants in North America, it is otherwise with the vast accumulations of coal in that country.

“The true coal,” says Dr. Dawson, “consists principally of the flattened bark of Sigillarioid and other trees, intermixed with leaves of Ferns and Cordaites, and other herbaceous debris, and with fragments of decayed wood, constituting ‘mineral charcoal,’ all these materials having manifestly alike grown and accumulated where we find them."[1]

[Footnote 1:  “Acadian Geology,” 2nd edition, p. 138.]

When I had the pleasure of seeing Principal Dawson in London last summer, I showed him my sections of coal, and begged him to re-examine some of the American coals on his return to Canada, with an eye to the presence of spores and sporangia, such as I was able to show him in our English and Scotch coals.  He has been good enough to do so; and in a letter dated September 26th, 1870, he informs me that—­

“Indications of spore-cases are rare, except in certain coarse shaly coals and portions of coals, and in the roofs of the seams.  The most marked case I have yet met with is the shaly coal referred to as containing Sporangites in my paper on the conditions of accumulation of coal (Journal of the Geological Society, vol. xxii. pp. 115, 139, and 165).  The purer coals certainly consist principally of cubical tissues with some true woody matter, and the spore-cases, &c., are chiefly in the coarse and shaly layers.  This is my old doctrine in my two papers in the Journal of the Geological Society, and I see nothing to modify it.  Your observations,