490 



NATURE 



{March 27, 1879 



GEOGRAPHICAL EVOLUTION^ 



IN the future development of scientific geography one 

 of the main lines of advance will be in the direction 

 of a closer alliance with geolog>'. The descriptions of 

 the various countries of the globe will include an account 

 of how their present outlines came into existence, and 

 how their plants and animals have been introduced and 

 distributed. The principles on which this evolutional 

 geography will be founded have regard to the materials 

 of which the framework of the land consists, to the 

 various ways in which these materials have been built up 

 into the solid crust of the earth, and to the superficial 

 changes to which they have been subsequently exposed. 

 The materials of the land consist mainly of compacted 

 detritus, which, worn from previously existing terrestrial 

 surfaces, has lieen laid down in the sea. Hence the 

 land, as we now see it, has originated under the sea. But 

 the common belief that over the whole globe land and 

 sea have been continually changing places, and that wide 

 continents may have bloomed even over the site of the 

 most lonely abysses of the ocean, may be shown to be 

 incorrect by a consideration of the character of the sedi- 

 mentary rocks of the land on the one hand, and of 

 that of the deposits of the sea-floor on the other. 

 The sedimentary rocks, even in the most massive 

 palaeozoic formations where they attain depths of 

 several miles, are shallow-water deposits, formed out of 

 the waste of the land and always laid down near land. 

 Nowhere among them, even including the thick organi- 

 cally-derived limestones, such as the chalk, is there any 

 formation which properly deserves to be considered that 

 of a deep sea. Recent researches into the nature of the 

 sea-bottom across the great ocean-basins have likewise 

 shown that the deposits there in progress have no real 

 analogy among the rocks of the land. The conclusion to 

 t>e drawn from the evidence is that the g^eat ocean-basins 

 have always existed, and that the terrestrial areas have 

 also lain on the whole over those tracts where they still 

 exist. 



The way in which the sedimentary rocks have been 

 tilted up and made to lie discordantly on each other 

 shows that the marginal belt of sea-floor near the land 

 has again and again been upraised and worn down. The 

 ocean-basins appear from very early times to have been 

 areas of subsidence, while the continental elevations 

 have been lines of relief from the strain of terrestrial 

 contraction. The land has been subjected to periodic 

 movements of upheaval, sometimes of great violence, 

 whereby not only large areas of sea-bottom were raised 

 into land, but where, as huge earth-waves, lines of moun- 

 tain-chain were ridged up. During these movements 

 great changes were effected in the structure and arrange- 

 ment of the rocks in the regions affected, original sedi- 

 mentary masses being rendered crystalline, and even 

 reduced to such a pasty or fluid condition as to be 

 squeezed into rents of the more solid superincumbent 

 rocks. Volcanic orifices were likewise opened, by which 

 communication was established between the heated 

 interior and the surface. The relative dates of these 

 successive terrestrial disturbances can be satisfac- 

 torily determined by stratigraphical and pateontological 

 evidence. 



The history of the gradual growth of the European 

 continent furnishes many interesting and instructive 

 illustrations of the principles by which evolutional geo- 

 graphy is to be worked out. The earliest European land 

 appears to have existed in the north and north-west, 

 comprising Scandinavia, Finland, and the north-west of 

 the British area, and to have extended thence through 

 boreal and arctic latitudes into North America. Of the 

 height and mass of this primeval land some idea may be 



' Abstract of an Address given by Prof. Geikie, F.R.S., at the meeting of 

 the Royal Geographical Society on March 24, 1879. 



formed by considering the enormous bulk of the material 

 derired from its degradation. In the Silurian formations 

 of the British Islands alone there is a mass of rock, worn 

 from that land, which would form a mountain-chain ex- 

 tending from Marseilles to the North Cape (i,8oo miles), 

 with a mean breadth of over 33 miles and an average 

 height of 16,000 feet, or higher than Mont Blanc. The 

 Silurian sea which spread across most of Central Europe 

 into Asia suffered great disturbance in some regions 

 towards the close of the Silurian period. It was 

 ridged up into land inclosing vast inland basins, the 

 areas of some of which are still traceable across the 

 British Islands to Scandinavia and the west of Russia. 

 An interesting series of geographical changes can be 

 traced during which the lakes of the Old Red Sand- 

 stone were effaced, the sea that gradually over- 

 spread most of Europe was finally silted up, and 

 the lagoons and marshes came to be densely crowded 

 with the vegetation to which we owe our coal-seams. 

 Later terrestrial movements led to the formation of 

 a series of bitter lakes across the heart of Europe like 

 those now existing in the south-east of Russia. Suc- 

 cessive depressions and elevations brought the open 

 sea again and again across the continent, and gave rise 

 to the accumulation of the rocks of which most of the 

 present surface consists. In these movements the growth 

 of the Alps and other dominant lines of elevation can be 

 more or less distinctly traced. It was at the close of the 

 Eocene period, however, that the great disturbances took 

 place to which the European mountains chiefly owe their 

 present dimensions. In the Alps we see how these move- 

 ments led to the crumpling up and inversion of vast piles 

 of solid rock, not older in geological position than the soft 

 clay which underlies London. Considerable additional 

 upheaval in Miocene times affected the Alpine ridges, 

 while in still later ages the Italian peninsula was broadened 

 by the uprise of its sub-Apennine ranges. The proofs of 

 successive periods of volcanic activity during this long 

 series of geographical revolutions are many and varied. 

 So too is the evidence for the appearance and disappear- 

 ance of successive floras and faunas, each no doubt seem- 

 ing at the time of its existence to possess the same aspect 

 of antiquity and prospect of endurance which we naturally 

 associate with those of our own time. The law of pro- 

 gress has been dominant among plants and animals 

 and not less upon the surface of the planet which they 

 inhabit. It is the province of the biologist to trace the 

 one series of changes ; of the geologist to investigate the 

 other. The geographer gathers from both the data which 

 enable him to connect the present aspects of Nature with 

 those out of which they have arisen. 



GEOGRAPHICAL NOTES 



At a recent meeting of the Board intrusted by the 

 French Government with the care of granting missions for 

 exploring foreign countries, it was decided that none of 

 the regions proposed offered any special field for excep- 

 tional services rendered to science. The funds of the 

 Government will be spent neither in exploring Central 

 Africa nor in seeking the north pole, but in excavating 

 Trojan ruins and examining some of the islands of the 

 Asian Archipelago. It was also complained that no 

 qualified traveller had been sent into civilised parts to 

 study the progress of special arts and sciences. Such 

 excursions as the celebrated " Voyage en Angleterre et 

 en Irlande," accomplished by Baron Dupin in 1820 have 

 rendered imm-ense services to French industry, and the 

 memory of it is not extinguished by the sixty years which 

 elapsed. The sending of regular scientific missions abroad 

 was inaugurated in France by the First Republic, for the 

 purpose, not exclusively for cultivating anthropology, but 

 for introducing into France the progress made by the 

 foreign nations. 



