KNOWLEDGE 



[Jantjaby 1, 1898. 



words in regard to the permanence or otherwise of the 

 great oceanic basins and continental areas of the globe. 

 This subject, it need scarcely be said, has not only an 

 intense and absorbing interest of its own — for it is difficult 

 for anyone except a geologist to fully realize that the solid 

 ground on which he stands may have been buried fathoms 

 deep beneath the water — but is also one of the utmost 

 importance in regard to many puzzling problems connected 

 with the present and past geographical distribution of 

 terrestrial animals and plants on the surface of the globe. 



Although it might well have been thought that opinion 

 in matters scientific would be unlikely to veer suddenly 

 round, and after tending strongly in one direction incline 

 with equal force in the one immediately opposite, yet 

 there are few instances where the swing of the pendulum 

 of opinion to one side has been more swiftly followed by its 

 oscillation to the other than has been the case in the 

 problem of the permanency of continents and oceans. 

 When geology first began to take rank among the exact 

 sciences, and it was demonstrated that most of the shells 

 and other fossils found in the solid rock of many of our 

 continents and islands were of marine origin, it was a 

 natural, if hasty, conclusion that land and sea had been 

 perpetually changing places, and that what is now the 

 centre of a continent might comparatively recently have 

 been an ocean abyss. Accordingly, when any difficulty 

 in finding an adequate explanation in regard to the 

 geographical distribution of the animals or plants of two 

 or more continents or islands occurred, the aid of an 

 " Atlantis " or a " Lemuria " was at once invoked without 

 misgiving, and a path thus indicated across which the 

 inhabitants of olie isolated area could easily have passed to 

 another. 



This was one swing of the pendulum. But as the 

 methods of geological observation and investigation became 

 more exact and critical, it was soon obvious that, in many 

 areas at least, the alternations between sea and land could 

 not have been so frequent or so general as had been at 

 first supposed. It was, indeed, perfectly true that many 

 portions of some of our present continents had for 

 long periods been submerged, or had been at intervals 

 alternately land and sea. But at the same time it began 

 to be realized that the fossiliferous marine deposits 

 commonly met with on continents and large islands were 

 not of such a nature that they could have been laid down 

 in depths at all comparable to those now existing in certain 

 parts of the basin of the Atlantic. Even a formation like 

 our English chalk, which had been supposed to have 

 analogies with the modern Atlantic deposits, appears to 

 have been laid down in a sea of much less depth and 

 extent, and probably more nearly comparable with the 

 modern Mediterranean. Then, again, it was found that 

 large tracts in some of our present continents, such as 

 Africa and India, had existed as dry land throughout a 

 very considerable portion of geological time. Moreover, it 

 was asserted that no formations exactly comparable to those 

 now in course of deposition in the ocean abysses could be 

 detected in any of our existing continents or islands ; while 

 it was further urged that in none of the so-called oceanic 

 islands (that is, those rising [from great depths at long 

 distances from the continental areas) were there either 

 fossiliferous or metamorphic rocks similar to those of the 

 continents and larger continental islands. 



This was the second swing of the pendulum, and for a 

 long period it was confidently asserted that where con- 

 tinents now exist there had never been any excessive 

 depth of ocean ; and, conversely, that in the areas now 

 occupied by the great ocean abysses there had never been 

 land during any of the later geological epochs. It was, 



indeed, practically affiimed that wherever the sounding- 

 line indicates a Ihcusand fathoms or more of water, there 

 sea had been practically always, and that no part of the 

 present continents bad ever been submerged to anything 

 like that depth. 



Almost as soon as the pendulum of opinion bad attained 

 the full limits of its swing in this direction (and this swing 

 had been largely due to the influence of geologists and 

 physicists), there began to be signs of its return to a less 

 extreme position. It was, in the first place, proved that 

 a few deposits — and these of comparatively recent date — 

 analogous to those of the ocean abysses, do occur in 

 certain areas. And, in the second place, it was shown 

 that a few oceanic islands do contain rocks like those 

 of the continents, and are not solely of volcanic or 

 organic origin. Zoological and palfeontological discoveries 

 were at the same time making rapid advances ; and the 

 students of these branches of science, who had been 

 among the foremost in giving the swing of the pen- 

 dulum on the side of continental instability its first 

 impulse, now began to press their views — only in a 

 more moderate manner — in the same direction. Evidence 

 had long been accumulating as to the identity of certain 

 freshwater formations and their included animal and plant 

 remains occurring in South America, South Africa, India, 

 and Australia ; and it was urged that during the Secondary 

 period of geological history not only was Africa connected 

 with India by way of Madagascar and the Seychelles, 

 but that laud extended across what is now the South 

 Atlantic to connect the Cape with South America, and 

 that probably India was likewise joined to Australia by 

 way of the Malay archipelago and islands. In fact, there 

 seems good evidence to indicate that at this early epoch 

 there was a land girdle in comparatively low latitudes 

 encircling some three-fourths of the earth's circumference 

 from Peru to New Zealand and Fiji. 



Even taking into account the comparatively early date 

 of its existence, this girdle of land, the evidence in favour 

 of which can scarcely be shaken, gave a heavy blow to 

 the adherents of the absolute permanency of continents 

 and oceans, as it clearly indicates the comparatively 

 modern origin of the basin of the South Atlantic. But this 

 is not all. South America, which there is good evidence 

 to believe was long cut off from the northern half of the 

 New World, shows certains indications of affinity in its 

 fauna with that of Europe in early Tertiary times, and to 

 a certain extent with that of modern Africa ; and the only 

 satisfactory way of explaining these relationships is by 

 assuming either the persistence of the land connection 

 between the Cape and South America across the South 

 Atlantic till a comparatively late geological epoch, or that 

 such connection took place further south by means of the 

 Antarctic continent. There are several objections, which 

 need not be considered here, in regard to the latter alter- 

 native ; and since there is other evidence in favour of the 

 comparatively recent origin of the South Atlantic depres- 

 sion, the persistence of a land connection in lower latitudes 

 seems the more probable explanation. 



In addition to all this, there is evidence of a more or 

 less intimate relationship between the land faunas of 

 Australasia and South America ; and as similar types are 

 not met with in Africa, and several of them belong to 

 groups unlikely to have endured Antai'ctic cold, it has 

 been suggested that America and Australasia were in 

 connection at no very remote epoch by way of the Coral 

 Sea. It is known, for instance, that some of the Australian 

 marsupials are more or less closely allied to others which 

 inhabited South America before it was connected with 

 North America ; and as no kindred types are met with 



