84 



HARDWICKE'S SCIENCE-GOSSIP. 



iome mistakes on the road? Where they have 

 ventured, others will soon follow and the errors of 

 those original thinkers who have been to science 

 what Columbus was to navigators and Galileo to 

 astronomers, will not even dim the lustre of their 

 glory. When will a great botanist stand forth and 

 hew out a road for us, never heeding scratches and 

 bruises and inevitable mistakes, but content if he has 

 only pointed the way to the goal, which other men 

 will reach ? Alas ! in the year of grace, 1888, when 

 we take up a so-called " Geological History of 

 Plants," we find it written by an eminent botanist 

 indeed, but also by one of the fast diminishing band 

 of anti-evolutionists. Can any one even imagine a 

 "Geological History of Animals," written from an 

 anti-evolutionist point of view at this date ? So 

 strong in some places is the evidence for evolution 

 by a mere statement of bare facts, that Sir J. W. 

 Dawson is obliged to explain that his remarks are 

 " not to be taken in a Darwinian sense." He even 

 thinks that, after "specific types have been created, 

 they may, by the culture of their Maker, be ' sported ' 

 into new varieties or sub-species." If the changes in 

 plants came about as they have done in animals, then 

 "sports " can have very little to do with creating new 

 varieties or species. Man truly avails himself dexter- 

 ously of so-called " sports," as in the familiar case of 

 the Ancon breed of sheep. But nature in forming 

 new species, if we are to believe the evidence of 

 palaeontology, or even the slow changes going on 

 before our eyes, does not work by "sports." She 

 effects her changes by almost imperceptible degrees ; 

 a tooth, for instance, first retarded in its develop- 

 ment, then losing a cusp, then appearing only 

 occasionally, and slowly vanishing altogether. Such 

 changes need not be sought for in fossiliferous rocks ; 

 they are going on at this day in the teeth of civilised 

 man, as they once took place in the ancestors of the 

 camel, the cat, and the dog. 



But as a practical palaeo-botanist. Sir J. W. 

 Dawson has perhaps no superior, and much may be 

 learned of vivid interest from his "Geological 

 History of Plants." 



In the massive rocks of Laurentian and Huronian 

 age, whose united depths have been estimated at 

 fifty thousand feet, no undoubted fossils have been 

 found. Imagination utterly fails when we try to 

 form an idea of the stupendous cycles of time, which 

 must have elapsed during the deposition of these 

 tremendous masses, or to picture to ourselves the 

 condition of the globe. Science allows us to imagine 

 oceans almost at boiling-point ; violent eruptions of 

 the still hot crust of our planet ; tides which would 

 have swept away the inhabitants of the Midlands of 

 England, had so insignificant a speck of land as 

 England then existed. In the lower part of the 

 Laurentian rocks, thirty thousand feet thick, there is 

 no trace of the existence of any living thing. But in 

 the middle portion of the Laurentian, great beds of 



limestone, of graphite and of iron-ore are found. In 

 more recent formations, deposits of this nature in- 

 fallibly point to the existence of animal and vegetable 

 life, but it is impossible to pronounce whether the 

 condition of our globe in Laurentian times would or. 

 would not have allowed of the independent deposition 

 of these minerals. Sir J. W. Dawson strongly inclines 

 to the belief that the graphite of the Laurentian 

 rocks is of vegetable origin, and if this be so, the 

 vegetation must have been profuse, though probably 

 of the lowest type, consisting of cellular plants, such 

 as algK, mosses, and lichens, or of organic carbon 

 compounds of a lower type than any protoplasm now 

 existing. 



The quantity of graphite in the lower Laurentian 

 series is enormous. " In the Green Lake limestone ; 

 on the Ottawa river the vertical thickness of the 

 veins of graphite is estimated at from twenty-five tor 

 thirty feet thick. At one place in this district a bed 

 of graphite, from ten to twelve feet thick and yielding 

 twenty per cent, of the pure material, is worked. As 

 it appears in the excavation made by the quarryman, 

 it resembles a bed of coal. When it is considered 

 that graphite occurs in similar abundance at several 

 other horizons, in beds of limestone, thirty-five 

 hundred feet thick, it is scarcely an exaggeration to 

 maintain that the quantity of carbon in the Lauren- 

 tian is equal to that in the carboniferous system." 



In the Silurian and Devonian formations, bitumin ■ 

 ous shales and limestones have been metamorphosed 

 by extreme heat and pressure and converted into 

 graphitic rocks not very dissimilar to those in the 

 less altered portions of the Laurentian. "In the 

 Quebec rocks of Point Levi, veins more than a foot 

 thick, are filled with a coaly matter having a 

 transverse columnar structure regarded by Logan 

 and Hunt as an altered bitumen." It is probable 

 that the Laurentian graphite, if of vegetable origin-, 

 was thoroughly "disorganised and bituminised before 

 its change into graphite." 



The climate and atmosphere of Laurentian times 

 may have been well fitted for the development of low 

 organic life. Vast quantities of carbon dioxide after- 

 wards sealed up in limestones and carbonaceous beds 

 must have still floated in the atmosphere, and given 

 rich nourishment to vegetable tissues. The internal 

 heat of the earth would still warm the waters of the 

 sea, and the whole world must have resembled the 

 very hottest of tropical green-houses. Sir J. W^ 

 Dawson thinks that towards the close of this period, 

 algae may have attained gigantic dimensions, and 

 " may even have ascended out of the water in some 

 of their forms." The lowly " cellular and tabular 

 plants now occupying humble positions as flat lichens, 

 or slender cellular mosses, may have been so strength- 

 ened and modified as to constitute forest trees. . . ." 

 A little later in this history we shall see evidence in 

 the flora of the Silurian of a survival of such forms. 

 ( To be continued.') 



