August 12, 1897] 



NATURE 



;-5i 



SOME PROBLEMS OF ARCTIC GEOLOGY.^ 



II. Former Arctic Climates, 

 T N a summary of the geological history of the Arctic Ocean 

 -'- {ante, p. 301) it was remarked that in Silurian times the 

 water was warmer than it is at the present day ; and there 

 is no doubt that the climate of the Arctic regions has varied 

 greatly. According to the belief generally accepted there have 

 been periods when the climate of the northern hemisphere was 

 so severe that an ice sheet extended from Ireland to Siberia, 

 from the Thames Valley to the North Pole ; and then at other 

 times, as the whole earth enjoyed the doubtful benefits of a 

 tropical climate, Greenland's now icy mountains were bordered 

 by a coral strand. This view of the great variation of Arctic 

 temperature has been so widely held that it has exercised a very 

 jjreat influence on theories of faunal migrations and on the 

 former climates of the world. The volumes which summarise 

 the results of the Challenger expedition show to what an extent 

 ^ome of the latest speculations as to climatic change have been 

 influenced by this theory ; for in that work Dr. Murray strongly 

 advocates Blandet's suggestion that in late Palaeozoic limes 

 there was "over the. whole globe an almost complete equality 

 in the distribution of light and heat" due to the "very much 

 greater size of the sun in the early stages of the earth's history." 

 And this bigger Palwozoic sun was assumed in order to explain 

 the fact that " the Arctic Ocean was a coral sea in Carboniferous 

 times." 



Let us, therefore, briefly consider how far the evidence of 

 Arctic geology supports the statements that have been based 

 upon it in this respect. The theory that the Arctic regions 

 once enjoyed a tropical climale was first advanced on the evidence 

 •of some fossil plant beds, of which the most famous occur in 

 Disco Island and neighbouring parts of the coast of Greenland. 

 The fossil plants from these beds were described by Heer, 

 ^vhose conclusions have been summarised by Lyell as follows : — 

 "In this rich flora considerably more than half are trees, which is 

 the more remarkable since trees do not exist in any part of Green- 

 land even 10" further south. More than fifty species of Coniferre 

 have been found with species of Thujopsis and Salisburia now 

 peculiar to Japan. There are also beeches, oaks, planes, poplars, 

 maples, walnuts, limes, and even a magnolia. Among the 

 shrubs were many evergreens, as Andromeda and two extinct 

 genera, Daphno^ene and M'Clintockia, with fine leathery 

 leaves ; together with hazel, blackthorn, holly, logwood and 

 hawthorn. Potamogeton, Sparganium and Menyanthes grew 

 in the swamps ; while ivy and vines twined around the forest 

 trees, and broad-leaved ferns grew beneath their shade. Such 

 a vigorous growth of trees within 12" of the pole, where now a 

 dwarf willow and a few herbaceous plants form the only vege- 

 tation, and where the ground is covered with almost perpetual 

 snow and ice, is truly remarkable." 



These statements were so positively made and so fascinatingly 

 sensational, that they have been repeated in every text-book, 

 while the protests against them have been generally ignored. 

 Protests, however, have been often made. The first botanist to 

 visit the Disco plant beds was the late Dr. Robert Brown ; and 

 as the result of his investigations he wrote — "I must protest 

 against the way in which Prof. Heer has been making species 

 and genera out of these fossils with a recklessness regardless of 

 con>equences." Mr. Starkie Gardner checked a long series of 

 Heer's determinations, and declared them valueless ; he re- 

 marked that Heer's conclusions were "based upon specimens 

 too fragmentary to be of any value, and belong to types of 

 leaves which are so universal that they would, even if perfect, 

 fall into the undeterminable residuum of a fossil flora. ' He 

 concluded that at least half of these genera and species of 

 Heer's must be suppressed. 



Prof. Nathorst, in whose care Heer's type specimens are now 

 resting, is fortunately undertaking a careful revision of the 

 evidence, and he is as emphatic as Brown and Gardner regarding 

 the unsatisfactory nature of Heer's identifications. 



The most important point in this reduction of Heer's species, 

 is that it is the plants which are most indicative of the tropical 

 conditions, such as the palms, which have to be abandoned. 

 That many big-leaved plants grew in areas which now support 

 only an insignificant growth of saxifrages and crucifers, is 

 undeniable ; and the leaves in question often present resem- 

 blances to those of trees, such as the plane, maple and lime. 

 But palaeobotatiists now distrust the evidence of leaves alone, 



• Concluded from page 303. 



which are. moreover, especially untrustworthy in the Arctic 

 regions. If a specimen of a Norwegian shrub that has grown 

 at Tromso be compared with a specimen of the same species 

 that has grown at Christiania, the former will be seen to have 

 less wood but larger leaves. The continual daylight in the 

 summer has a very stimulating effect on leaf production, and the 

 leaves are larger and fleshier than they would be if once a day 

 their growth were stopped by night. 



But it may be said, this will not explain the occurrence of 

 the great tree stems which are found in association with the Arctic 

 coal seams and leaf beds. It was mainly to explain the growth 

 of these tree trunks that Sir John Evans introduced his well- 

 known theory of the shifting of the pole ; for at one time it was 

 held that an annual exposure for three months to continuous 

 darkness would have been quite inhibitory to the growth of trees. 

 Botanists, however, now tell us that in a cold climate the winter's 

 darkness would be an advantage to vegetation instead of a fatal 

 objection ; and the darkness is actually secured artificially in the 

 gardens of St. Petersburg as a protection to trees. Trees even 

 now do grow beyond the Arctic Circle, and tha darkness is no 

 absolute bar to their having ranged many degrees further north. 

 That pines and other conifers did so in the past is proved both 

 by the mode of occurrence of the fossils and by the histological 

 structure of the wood. But that all the trees found buried in 

 the rocks of Spitsbergen and Greenland grew where they now 

 occur is by no means so certain. It is probable that most of 

 them have been carried to their present latitude as drift wood. 

 The famous Forest B.-d at Cromer was so named in the belief 

 that it was the site of an old forest ; but it is now regarded as 

 an estuarine deposit, formed at some distance from the place 

 where the trees that occur in it grew. Similarly, the description 

 given by Brainerd of the petrified forest found in the north of 

 Greenland by the Greeley expedition is as consistent with the 

 view that the tree trunks were drifted as that they grew in situ. 

 In the case of the Disco leaf beds we fortunately have the 

 opinion of a trained botanist, the late Robert Brown. He 

 examined the plant beds especially in reference to this point, and 

 he tells us that not " in any instance did I find the leaves in 

 conjunction with or attached to the stem, by which I could 

 positively say that these were the leaves of the tree to which the 

 stem belonged, or that the stem was brought there, or was in 

 any way connected with the same natural or physical causes 

 which influenced the leaves." Brown quotes, and apparently 

 approves, Steenstrup's remarks, "perhaps they [the leaves] 

 were blown by the wind to their present locality." Sj Brown 

 saw no evidence that the West Greenland plant bads mark the 

 site of ancient forests. 



The quantity of drift wood cast upon the Arctic shores is 

 enormous. Many raised beaches are strewn with pine and 

 larch logs, to which the roots are often attached and are buried 

 in the mud. Mosses and sedges, willows and saxifrages grow 

 upon the beach ; their remains, together with wind-borne 

 material, may gradually fill up the spaces between the tree 

 trunks, and the whole may be buried by rainwash from cliffs 

 above the beach, or by tide-borne sand should tha be.ich again 

 sink below sea-level. Under such circumstances an impure coal 

 seam would be formed ; and a future geologist might easily be 

 deceived by the numerous tree trunks, and the rich leaf remiins, 

 into the belief that at the era of its formation the locality had 

 supported a forest growth, which could not now be paralleled 

 less than 20" further south. 



Most of the Arctic drift wood consists of logs of pine and 

 larch from the Siberian forests ; but blocks of mahogany from 

 Central America sometimes occur, and West Indian beans are 

 not uncommon. Hence the occasional presence of tree stems 

 of tropical types may easily be explained without assuming any 

 great change of climate. But the action of ocean currents is not 

 the only factor thit may have complicated the evidence of these 

 northern plant beds. Many limitations are necessary in the 

 application of fossils to the elucidation of former climates. 

 Genera that once lived in cold regions may now be restricted to 

 the tropics owing to a change in habit ; and plants that were 

 once world-wide in distribution mav now survive only in a few 

 especially favourable localities. Thus in the Carboniferous 

 period the most abundant ferns belonged to the order 

 Marattiaceai, of which there are twenty-seven living species ; 

 twenty-two of these occur in the torrid zone, three in the south 

 temperate zone, two in the north temperate zone, and there are 

 none in the frigid zone. This does not prove that, wherever 

 Marattiacese are found in carboniferous rocks, the climate was 



NO. 1450. VOL. 56] 



