Sept. 6, 1883] 



NA TURE 



453 



nucleus by decay and aqueous erosion, and when we take into 

 account the greater local thickness of sediments towards the 

 present sea-basins, we can scarcely avoid the conclusion that 

 extensive areas once occupied by high land are now under the 

 sea. But to ascertain the 1 recipe areas and position of these 

 perished lands may now be impos ible. 



In point of fact, we are obliged to believe in the contempora- 

 neous existence in all geological periods, except perhaps the 

 very oldest, of three sorts of areas on the surface of the earth : 

 I. Oceanic areas of deep sea, which must always have occupied 

 the bed of the present ocean, or parts of it; 2. Continental 

 plateaus, sometimes existing as low flats or as higher tablelands, 

 and sometimes submerged ; 3. Areas of plication or folding, 

 more especially along the borders of the oceans, forming elevated 

 lands rarely submerged, and constantly affording the material of 

 sedimentary accumulations. 



Every geologist knows the contention which has been 

 occasioned by the attempts to correlate the earlier palaeozoic 

 deposits of the Atlantic margin of North America with those 

 forming at the same time on the interior plateau, and with those 

 of intervening lines of plication and igneous disturbance. 

 Stratigraphy, lithology, and fossils are all more or less at fault 

 in dealing with these questions ; and, while the general nature of 

 the problem is understood by many geologists, its solution in 

 particular cases is still a source of apparently endless debate. 



The causes and mode of operation of the great movements of 

 the earth's crust which have produced mountains, plains, and 

 tablelands, are still involved in some mystery. One patent cause 

 is the unequal settling of the crust towards the centre ; but it is 

 not so generally understood as it should be that the greater 

 settlement of the ocean bed has necessitated its pressure against 

 the sides of the continents in the same manner that a huge ice- 

 floe crushes a ship or a pier. The geological map of North 

 America shows this at a glance, and impresses us with the fact 

 that large portions of the earth's crust have not only been folded, 

 but bodily pushed back for great distances. On looking at the 

 extreme north, we see that the great Laurentian mass of central 

 Newfoundland has acted as a protecting pier to the space 

 immediately west of it, and has caused the Gulf of St. Lawrence 

 to remain an undi-turbed area since palceozoic times. I mmediately 

 to the south of this, Nova Scotia and New Brunswick are folded 

 back. Still farther south, as Guyot has shown, the old sediments 

 have been crushed in sharp folds against the Adirondack mass, 

 which has sheltered the tableland of the Catskills and of the 

 Great Lakes. South of this again, the rocks of Pennsylvania 

 and Maryland have been driven back in a great curve to the 

 west. Nothing, I think, can more forcibly show the enormous 

 pressure to which the edges of the continents have been exposed, 

 and at the same time the great sinking of the ocean beds. Com- 

 plex and difficult to calculate though these movements of plica- 

 tion are, they are more intelligible than the apparently regular 

 pulsations of the flat continental areas, whereby they have 

 alternately been below and above the waters, and which must 

 have depended on somewhat regular recurring causes, connected 

 either with the secular cooling of the earth, or with the gradual 

 retardation of its rotation, or with both. Throughout these 

 changes, each successive elevation exposed the rocks for long 

 ages to the decomposing influence of the atmosphere. Each 

 submergence swept away, and deposited as sediment, the material 

 accumulated by decay. Every change of elevation was accom- 

 panied with changes of climate and with modifications of the 

 habitats of animals and plants. Were it possible to restore ac- 

 curately the physical geography of the earth in all these respect-, 

 for each geological period, the data for the solution of many 

 difficult questions would be furnished. 



It is an unfortunate circumstance that conclusions in geology 

 arrived at by the most careful observation and induction do not 

 remain undisturbed, but require constant vigilance to prevent 

 them from being overthrown. Sometimes, of course, this arises 

 from new discoveries throwing new light on old facts ; but when 

 this occurs it rarely works the complete subversion of previously 

 received views. The more usual case is, that some over-zealous 

 specialist suddenly discovers what seems to him to overturn all 

 previous beliefs, and rushes into print with a new and plausible 

 theory, which at once carries with htm a host of half-in- 

 formed people, but the insufficiency of which is speedily made 

 manifest. 



Had I written this address a few years ago, I might have 

 referred to the mode of formation of coal as one of the things 

 most surely settled and understood. The labours of many 



eminent geologists, microscopists, and chemists in the Old and 

 the New Worlds had shown that coal nearly always rests upon 

 old soil surfaces penetrated with roots, and that coal-beds have in 

 their roofs erect trees, the remains of the last forests that grew 

 upon them. Lrgan and I have illustrated this in the case of the 

 series of more than sixty successive coal-beds exposed at the 

 South Joggins, and have shown unequivocal evidence of land- 

 surfaces at the time of the deposition of the coal. Microscopical 

 examination has proved that these coals are composed of the 

 materials of the same trees whose roots are found in the under- 

 clivs and their stems a 1 d 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 accumulation ; and that, in this, ordinary coal 

 differs from bituminous shale, earthy bitumen, and some kinds 

 of cannel, which have been formed under v\ ater ; that the matter 

 remaining as coal consists almost entirely of epidermal tissues, 

 which, being suberose in character, are highly carbonaceous, very 

 durable, and impermeable by water, 1 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 American coal-fields, and seemed to leave no 

 doubt on the subject. But several years ago certain microscopisl s 

 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 forest', and because they contain suberose 

 matter of the same character with epidermal tissues generally. 

 Immediately we were informed that all coal consists of spores ; and, 

 this being at once accepted by the unthinking, the results of the 

 labours of many years are thrown aside in favour of this crude 

 and partial theory. A little later, a German microscopist lws 

 thought proper to describe coal as made up of minute algse, 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 eminent botanist of that country t > 

 revive the drift theory of coal, in opposition to that of growth in 

 siiu. A year or two ago, when my friend Professor Williamson 

 of Manchester imformed me that he was preparing 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 neces- 

 sary ; 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 labours. 



An illustration of a different character is afforded by the 

 controversy now raging with respect to the so-called fucoids of 

 the ancient rocks. At one time the group of fucoids, or alga. 1 , 

 constituted a general 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 under- 

 stood by botanists. Such a group was sure to be eventually 

 dismembered. The writer has himself done something toward 

 this," but Professor Natho^t has done still more ; 3 and now 

 some intelligible explanation can be given of many of these forms. 

 Quite recently, however, the Count de Saporta in an elaborate 

 illustrated memoir, 4 has come to the defence of the fucoids, more 

 especially against the destructive experiments of Nathorst, and 

 would carry brick into the vegetable kingdom many things which 

 would seem to be mere trails of animals. While writing this 

 address, I have received from Professor Crie of Rennes a paper 

 in which he not only supports the algal nature of Ru ichnites, 

 Arthrichnites, and many other supposed fucoids, but claims for 

 the vegetable kingdom even Receptaculites and Ai^neocyatbus. 

 It is not to be denied that some of the facts which he cites, 

 respecting the structure of the Siphoniae and of certain modern 

 incrusting alga-, are very suggestive, though I cannot agree with 

 his conclusions. My own experience has convinced me that, 

 while non-botanical geologists are prone to mistake all kinds of 



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

 3 " Footprints and Impressions on Carboniferous Rocks," Awer. Jourti. 

 Sc, 1873. 



3 Royal Swedish Academy, Stockholm. 1881. 

 < " Apropos des Algues Fossiles." Paris, 1883. 



