66 THE POPULAR SCIENCE MONTHLY. 



of the same trees whose roots are found in the under-clays, and their 

 stems and leaves in the roof -shales ; that much of the material of the 

 coal has been subjected to sub-aerial decay at the time of its accumula- 

 tion ; and that in this, ordinary coal differs from bituminous shale, 

 earthy bitumen, and some kinds of cannel, which have been formed 

 under water ; that the matter remaining as coal consists almost en- 

 tirely of epidermal tissues, which, being suberose in character, are 

 highly carbonaceous, very durable, and impermeable by water,* and 

 are hence the best fitted for the production of pure coal ; and finally 

 that the vegetation and the climatal and geographical features of the 

 coal period were eminently fitted to produce in the vast swamps of 

 that period precisely the effects observed. All these points and many 

 others have been thoroughly worked out for both European and Ameri- 

 can coal-fields, and seemed to leave no doubt on the subject. But sev- 

 eral years ago certain microscopists observed on slices of coal layers 

 filled with spore-cases — a not unusual circumstance, since these were 

 shed in vast abundance by the trees of the coal-forests, and because 

 they contain suberose matter of the same character with epidermal 

 tissues generally. Immediately we were informed that all coal con- 

 sists of spores ; and, this being at once accepted by the unthinking, 

 the results of the labors of many years are thrown aside in favor of 

 this crude and partial theory. A little later, a German microscopist 

 has thought proper to describe coal as made up of minute algae, and 

 tries to reconcile this view with the appearances, devising at the same 

 time a new and formidable nomenclature of generic and specific names, 

 which would seem largely to represent mere fragments of tissues. 

 Still later, some local facts in a French coal-field have induced an emi- 

 nent botanist of that country to revive the drift theory of coal, in op- 

 position to that of growth in situ. A year or two ago, when my friend 

 Professor Williamson, of Manchester, informed me that he was pre- 

 paring a large series of slices of coal with the view of revising the 

 whole subject, I was inclined to say that, after what had been done by 

 Lyell, Goeppert, Logan, Hunt, Newberry, and myself, this was scarcely 

 necessary ; but, in view of what I have just stated, it may be that all 

 he can do will be required to rescue from total ruin the results of our 

 labors. 



An illustration of a different character is afforded by the contro- 

 versy now raging with respect to the so-called fucoids of the ancient 

 rocks. At one time the group of fucoids, or algae, constituted a gen- 

 eral place of refuge for all sorts of unintelligible forms and markings ; 

 graptolites, worm-trails, crustacean tracks, shrinkage-cracks, and, above 

 all, rill-markings, forming a heterogeneous group of fucoidal remains 

 distinguished by generic and specific names. To these were also added 

 some true land-plants badly preserved, or exhibiting structures not 

 well understood by botanists. Such a group was sure to be eventually 

 * " Acadian Geology," third edition, supplement, p. 68. 



