68 



NATURE 



\May 24, 1877 



of America as of Carboniferous age, simply because it 

 contains forms not found as yet in rocks so old in Eu- 

 rope. But this notion is at variance with stratigraphy 

 and animal fossils, and quite as wide of the mark as the 

 often-repeated dictum of some of the same authorities that 

 the Cretaceous flora of Vancouver Island and the 

 Eocene flora of the North-western plains are equivalents 

 of the European Miocene. In point of fact, we have in 

 America distinct floras of Erian and Carboniferous age 

 with an intermediate sub-flora of Lower Carboniferous 

 date,' and succeeding them the Triassic and Jurassic 

 flora, that of the Cretaceous, that of the Eocene, and that 

 of the Miocene ; and there is good reason to believe that 

 all of these invaded the Continent from the northward 

 and lingered longest in the south. There may no doubt 

 have been counter migrations from the south, but these 

 seem to have left less trace in the geological record. The 

 special Lower Carboniferous or "Culm" flora, and that 

 of the Eocene in Europe, may be of this character. 



If we compare these facts with those known from other 

 sources as to the alternation of cold and warm climates 

 in the northern hemisphere, it would seem that they 

 harmonise most closely on the hypothesis advocated by 

 Sir Charles Lyell, that these changes of climate have 

 depended mainly on the distribution of land and water 

 and of the ocean currents. 



Assuming a condition in which much tropical land 

 existed, along with islands in the Arctic and sub-Arctic 

 regions, surrounded with deep water over which warm 

 currents were distributed, a rich flora might extend as far 

 northward as the supply of light would permit. Further, 

 if such condition of equatorial protuberance were coin- 

 cident wiih a less obliquity of the ecliptic, there might be 

 less difficulty with regard to a continuous supply of light 

 than under present circumstances. Succeeding elevation 

 of northern and temperate land and depression of that 

 nearer the equator, would destroy the more southern flora 

 and cause that of the north to advance over the newly- 

 elevated continental plateaus. This would more especially 

 be the case if, as we may infer from the possible connec- 

 tion of equatorial subsidence with the retardation of the 

 earth's rotation, the depression of the northern land was 

 very slow and gradual, and that of the equatorial land 

 more sudden and paroxysmal. 



Invasions of plants from the north would thus result 

 from continental elevation in the temperate regions, and 

 these invasions would go on contemporaneously with the 

 introduction of less equable and cooler climatal conditions. 

 These might not, however, advance so far as to cause 

 extreme glacial phenomena, except in those, perhaps rare, 

 circumstances, when Arctic land was elevated while the 

 greater part of the tropical and temperate areas remained 

 under shallow seas with little heating and radiating sur- 

 face and invaded by much northern ice. Further, when 

 we take into consideration the growth of the continents 

 in later geological times, it is evident that such periods of 

 exceptional cold would be more likely to occur in these 

 later times, and that they might be less intense in earlier 

 geological periods, and might attain their maximum in 

 the last glacial period. They would also be irregular as 

 to the intervals between them, and might through long 

 periods be absent altogether. We have proof of the 

 efficacy of such causes in the contrast between the climates 

 of Labrador and England at the present day, and also in 

 that sameness of the climate of those regions in the Post- 

 pliocene period, of which I long ago pointed out the evi- 

 dence in my " Acadian Geology." Such moderate views 

 as to glacial periods may also serve to render more ex- 

 plicable the facts as to the absence of evidence of glacial 

 action in Arctic Tertiary formations as observed by 

 Nordenskjold. 



It will of course be understood that my conception of 

 glacial periods is not that of continental ice-caps ; but 

 ' Tweedian of North of England, Culm of Germany. 



rather such conditions as would cover great breadths of 

 shallow sea in the northern hemisphere with a permanent 

 and continuous ice-pack, accompanied of course with 

 "bordage" and "anchor ice" and with glaciers descend- 

 ing to the sea from high lands ; the whole resembling 

 that now occupying large areas of the Arctic seas, and 

 occurring in winter in the Gulf and River St. Laurence. 

 To such agencies I have been accustomed for the last 

 twenty years to refer our Canadian boulder clay and 

 glaciated rocks. Further, to this extent we have evi- 

 dence, locally at least, of ice-action in temperate latitudes 

 (in non-fossiliferous conglomerates with boulders) as far 

 back as the Huronian age, while the evidence of alternate 

 submergence and emergence of the northern land extends 

 down to that of the Post-pliocene, whose greatness geolo- 

 gists are only beginning to realise. 



It is a corollary from these views that there can have 

 been no change within geological time in the position of 

 the earth's axis of rotation. The distribution of sedi- 

 ment by the polar currents, and the lines of plication and 

 upheaval of the crust, as well as the distribution of suc- 

 cessive floras, prove that the poles have remained since 

 the Laurentian period where they now are. I need here 

 merely refer to the fact, well known to all American 

 geologists, that the earthy matter of the thick Appalachian 

 sediments lies parallel to the line of the modern Arctic 

 currents, which seem in all geological time to have been 

 potent agents in carrying the debiis of the disintegrated 

 Arctic rocks to the south, and filling up the voids caused 

 by equatorial subsidence. Further, the great organic 

 limestones, which represent the contemporaneous food- 

 bearing warm currents from the equator, lie on the pla- 

 teaus and in the bays of the old Eozoic and Palaeozoic 

 land. • 



We need not, however, in consistency with such views, 

 refuse to attach any importance which they may seem to 

 require to astronomical cycles affecting the eccentricity of 

 the earth's orbit and the precession of the equinoxes, or to 

 the possible diminution or inequality of solar energy, or 

 to the secular cooling and contraction of the earth or 

 the retardation of its rotation. But geologists and 

 palaeontologists, in speculating on past conditions of the 

 earth, should endeavour in the first instance to gauge the 

 value of the causes indicated by their own sciences ; and 

 where climate is in question no evidence can be more 

 important than that of continental elevation and depres- 

 sion, in connection with the appearance and diffusion of 

 those assemblages of land plants which furnish so sure 

 testimony as to climatal influences. 



I should perhaps apologise for throwing out these sug- 

 gestions with so little of illustration or proof. For much 

 of this I may refer to my published memoirs ; ' and I have 

 now before me a mass of additional evidence, collected 

 in all the great regions from Newfoundland to British 

 Columbia by several recent observers, which I have 

 not at the moment time or opportunity to throw into a 

 connected form. My present object is to invite the atten- 

 tion of the many young and active geologists now working 

 at these subjects to lines of investigation from which they 

 may be deterred by some of the theoretical views now 

 current. J. W. DAWSON 



McGill College, Montreal 



A NEW STIMULANT— PirURY 



BARON VON MUELLER writes to the Australian 

 Medical Journal on the origin of the Pitury, a 

 stimulant said to be of marvellous power, and known to 

 be in use by the Aborigines of Central Australia. After 

 years of efforts to get a specimen of the plant, he had 

 obtained leaves, but neither flowers nor fruits. He can 

 almost with certainty, after due microscopic examination, 



« Especially the Report above referred to, and " Notes on the Post- 

 pliocene Geology of Canada," Canadian Naturalist, New Series, vol. vi. 



