NOYEMBEE 1, 1892.] 



KNOWLEDGE 



217 



us to the question of " the permanence of ocean 

 basins," a doctrine that has been much discussed of 

 late years. The more extreme advocates of this theory 

 hold that the great oceanic depressions have, in the 

 main, always been depressions, and therefore below sea- 

 level, while the great land areas or continents have, in the 

 main, been always above sea-level. They only will allow 

 a certain amount of interchange between these two areas 

 along the margins of the continents where soundings are 

 shallow, and a slight elevation would make the sea bed dry 

 land, as, for instance, the North Sea. Without binding 

 ourselves down to this theory, we may admit that there is 

 evidence in its favour, but perhaps it is only true for the 

 deepest oceanic depressions. 



No one has yet succeeded in showing why either the 

 mountain chains or the broad folds of the continents and 

 the troughs of the oceans take the directions that have 

 somehow been given to them. The two land masses of the 

 new world. North and South America, trend north and south, 

 as do their mountain ranges. The Euro-Asiatic continent, 

 on the other hand, trends east and west, as does its main 

 axis of elevation, i.e., the great chain of mountains 

 beginning with the Pyrennees and ending with the Atlai 

 Mountains. Why are these things so? This is a problem 

 yet to be solved by the new geology, but at any rate it 

 would seem that the prevailing lines of elevation have been 

 determined at some very early period in the world's history, 

 probably in pre-geological times. 



Look at a map of the world, and you will see that the 

 great land masses, and some of the smaller ones too, all 

 point southwards. The most striking examples are North 

 and South America, Greenland, Africa ; but the same 

 rule applies to Scandinavia, Spain, Italy, Albania and 

 Greece, Arabia, India, Malacca, and even the two ends of 

 Australia. In some cases — as, for example, Scandinavia and 

 Italy — the reason is obvious, viz., the direction of mountain 

 ranges. But probably several causes have combined to 

 bring about this remarkable result. Perhaps ocean curi'ents 

 may be partly responsible, for in the southern hemisphere 

 there is a decided surface drift northwards, and perhaps 

 the currents wear away the ends of our continents. 



Prof. Suess, the leader of the new school of geology 

 in Vienna, questions the usually accepted doctrine that 

 continents are due to elevation, and thus strikes at 

 the root of ideas which, to most geologists, have 

 become axioms. He considers that we have no evidence 

 of any vertical elevation affecting wide areas such as 

 continents, and that the only movements of elevation that 

 take place are those by which mountains are upheaved. 

 Most geologists believe that the sea-level has remained 

 constant, as Lyell taught ; but Suess abandons this and 

 says that the water leaves the land, owing to changes in 

 sea-level, instead of the land leaving the water. This is 

 somewhat startling, and it will be interesting to see what 

 effect such teaching will have on English geologists. In 

 equatorial regions, according to Suess, the sea is gaining 

 upon the land, while in other latitudes the reverse would 

 appear to be the case. This is in harmony with his ^-iew 

 of a periodic flux and reflux of the waters of the ocean 

 between the equator and the poles. Another foreign 

 geologist, Schmick, beheves in grand secular movements 

 of the ocean in order to account for apparent elevation and 

 depression of land areas. These theories are a partial 

 revival and development of certain old-fashioned ^^ews 

 which, till lately, had been looked upon as quite out of 

 date. Thus, Celsius, 1.50 years ago, after examining the 

 coast lines of Sweden, came to the conclusion that the sea 

 had retreated from the land, owing to a gradual drying up 

 of the ocean. 



But to return to the present : we find our lands 

 distributed over the surface of a great continental plateau, 

 the edges of which plunge down more or less steeply into 

 the depths of the ocean, where some great depressions 



believe that the continental 

 oceanic depressions have never 

 the same time shore lines have 



so as to bring 



less magnitude, 



these two broad 



a kind of neutral 



exist. Most geologists 

 plateaux and the great 

 changed places. But at 

 advanced and retreated many times, 

 about geographical changes of more or 

 without causing a complete shifting of 

 features. Between them there is often 

 ground which may at one time be dry laud, at 

 another, sea. Let us now consider the relation between 

 coast lines and the slopes or margins of the great 

 plateaux. Eoughly speaking, our existing coast lines may 

 be said to trend in the same general direction as these 

 margins. It can be shown that there are two very distinct 

 types of coast line, and that they are determined by the 

 extent to which they correspond with the margins of the 

 plateaux. First we have coast lines of a simple type, 

 running for long distances in one general direction, and 

 not b);oken up into innumerable minor features. Of such 

 a kind are the east and west coast lines of Africa, or those 

 of the greater part of North and South America. Now in 

 these cases the coast lines are near to the steep slopes of 

 the several plateaux, so that a rise of several thousands of 

 feet would make very little change. The second type of 

 coast line is quite different ; instead of being regular, it is 

 very in-egular, nor does it run mainly in one direction. 

 They are broken up by promontories and peninsulas, by 

 inlets and fiords and islands. For example, we may take 

 the coast line of north-western Europe, or the correspond- 

 ing latitudes of North America. Here we have regions of 

 comparatively recent depression which has caused the sea 

 to come creeping over what before was land. Such regions 

 are partially submerged lands, the surface features of 

 which contribute to make the irregular coast lines. Thus 

 the fiords of Norway are simply land valleys submerged, 

 while the islands are hills partly submerged ; the same 

 appUes to the west coast of Scotland. An elevation of 

 north Europe, to the extent of 500 fathoms, would make 

 the sea go back to the margin of the European plateaux, 

 and give us a smooth and regular coast line about 200 

 miles west of the Ixish coast. These u-regular coast lines, 

 then, are due to surface features of the continental plateaux, 

 formerly made by atmospheric denudation, namely, hills 

 and valleys. A glance at a good physical map, showing 

 ocean contour lines, will show that they are regular and 

 of unbroken outline, except in those shallow seas that 

 really belong to the continental plateaux. 



Finally, the coast lines of the world's continents are of 

 very different ages ; some are young, born, as it were, of 

 yesterday, while others are of high geological antiquity. 

 Those of the Atlantic Ocean are very ancient, while those 

 bounding the Pacific are comparatively recent. Now this 

 explains why the latter ocean is bounded by high moun- 

 tain ranges, and the former only by low hiUs. These low 

 hills are the remnants of former great mountain ranges 

 worn down to mere stumps by ages of denudation. Thus 

 the hills of Devonshire, Wales, Scotland, and Norway are 

 known to be of very ancient date, and their geological 

 structure tells us that they are mere remnants of what 

 were once mighty ranges of mountains comparable with 

 the Alps or the Himalayas. We also know that formerly 

 volcanic action on a great scale took place along these old 

 ranges ; but that has died out, and they have reached a 

 state of stability or equilibrium. Along the margins of 

 the Pacific, however, we have a great circle of active 

 volcanoes acting along mountain ranges of great height, 



