August ii, 1892] 



NATURE 



35* 



interruptions along the Atlantic sea-board, the other traversing 

 Central Europe from west to east, and separating the area of the 

 Great Plain from the Mediterranean basin. The excessive 

 denudation which the more ancient lands have undergone, and 

 great uplifts of Mesozoic and of Cainozoic times, together with 

 the comparatively recent submergence of broad tracts in the 

 north and north-west, have not succeeded in obscuring the 

 dominant features in the architecture of our continent. 



I no%v proceed to trace, as rapidly as I can, the geographical 

 development of the coast-lines of the Atlantic as a whole, and 

 to point out the chief contrasts between them and those of the 

 Pacific. The extreme irregularity of the Arctic and Atlantic 

 shores of Europe at once suggests to a geologist a partially 

 drowned land, the superficial inequalities of which are account- 

 able for the vagaries of the coast-lines. The fiords of Norway 

 and Scotland occupy what were at no distant date land valleys, 

 and the numerous marginal islands of those regions are merely 

 the projecting portions of a recently sunken area. The conti- 

 nental plateau extends up to and a little beyond the one hundred 

 fathoms line, and there are many indications that the land for- 

 merly reached as far. Thus the sunken area is traversed by 

 valley-like depressions, which widen as they pass out to the 

 edge of the plateau, and have all the appearance of being hol- 

 lows of subaerial erosion. I have already mentioned the fact 

 that the Scandinavian uplands and the Scottish Highlands are 

 the relics of what were at one time true mountains of elevation, 

 corresponding in the mode of their formation to those of Swit- 

 zerland, and, like these, attaining a great elevation. During 

 subsequent stages of Palseozoic time, that highly elevated region 

 was subjected to long-continued and profound erosion — the 

 mountain country was planed down over wide regions to sea- 

 level, and broad stretches of the reduced land surface became 

 submerged. Younger Pal.xozoic formations now accumulated 

 upon the drowned land, until eventually renewed crustal dis- 

 turbance supervened, and the marginal areas of the continental 

 plateau again appeared as dry land, but not, as before, in the 

 form of mountains of elevation. Lofty table-lands now took 

 the place of abrupt and serrated ranges and chains — table-lands 

 which, in their turn, were destined in the course of long ages to 

 be deeply sculptured and furrowed by subaerial agents. During 

 this process the European coast-line would seem to have coin- 

 cided more or less closely with the edge of the continental 

 plateau. Finally, after many subsequent movements of the 

 crust in these latitudes, the land became partially submerged — 

 a condition from which North-western and Northern (Europe 

 would appear in recent times to be slowly recovering. Thus 

 the highly indented coast-line of those regions does not coincide 

 with the edge of the plateau, but with those irregularities of its 

 upper surface which are the result of antecedent subaerial 

 erosion. 



Mention has been made of the Russo-Germanic plain and the 

 Mediterranean as representing original depressions in the conti- 

 nental plateau, and of the high grounds that extend between 

 them as regions of dominant elevation, which, throughout all 

 the manifold revolutions of the past, would appear to have per- 

 sisted as a more or less well-marked boundary, separating the 

 northern from the southern basin. During certain periods it 

 was no doubt in some degree submerged, but never apparently 

 to the same extent as the depressed areas it served to separate. 

 From time to time uplifts continued to take place along this 

 central belt, which thus increased.in breadth, the younger forma- 

 tions, which were accumulated along the margins of the two 

 basins, being successively ridged up against nuclei of older 

 rocks. The latest great crustal movements in our continent, 

 resulting in the uplift of the Alps and other east and west ranges 

 of similar age, have still further widened that ancient belt of 

 dominant elevation which in our day forms the most marked 

 orographical feature of Europe. 



The Russo-Germanic basin is now for the most part land, the 

 Baltic and the North Sea representing its still submerged por- 

 tions. This basin, as already remarked, was probably never so 

 deep as that of the Mediterranean. We gather as much from 

 the fact that, while mechanical sediments of comparatively 

 shallow-water origin predominate in the former area, limestones 

 are the characteristic features of the southern region. Its rela- 

 tive shallowness helps us to understand why the northern de- 

 pression should have been silted up more completely than the 

 Mediterranean. We must remember also that for long ages it 

 received the drainage of a much more extensive land surface 

 than the latter — the land that sloped towards the Mediterranean 



NO. I 189, VOL. 46] 



in Palaeozoic and Mesozoic times being of relatively little im- 

 portance. Thus the crustal movements which ever and anon 

 depressed the Russo-Germanic area were, in the long run, 

 counterbalanced by sedimentation. The uplift of the Alps, the 

 Atlas, and other east and west ranges, has greatly contracted 

 the area of the Mediterranean, and sedimentation has also acted 

 in the same direction, but it is highly probable that that sea is 

 now as deep as, or even deeper than, it has ever been. It 

 occupies a primitive depression in which the rate of subsidence 

 has exceeded that of sedimentation. In many respects, indeed, 

 this remarkable transmeridional hollow — continued eastward in 

 the Red Sea, the Black Sea, and the Aralo-Caspian depression — 

 is analogous, as we shall see, to the great oceanic trough itself. 



In the earlier geological periods linear or axial uplifts and 

 volcanic action again and again marked the growth of the land 

 on the Atlantic sea-board. But after Palaeozoic times, no great 

 mountains of elevation came into existence in that region, while 

 volcanic action almost ceased. In Tertiary times, it is true, 

 there was a remarkable recrudescence of volcanic activity, but 

 the massive eruptions of Antrim and Western Scotland, of the 

 Fseroe Islands and Iceland, must be considered apart from the 

 general geology of our continent. From Mesozoic times on- 

 wards it was along the borders of the Mediterranean depression 

 that great mountain uplifts and volcanoes chiefly presented them- 

 selves. And as the land surface extended southwards from Cen- 

 tral Europe, and the area of the Mediterranean was contracted, 

 volcanic action followed the advancing shore-lines. The occur- 

 rence of numerous extinct and of still existing volcanoes along 

 the borders of this inland sea, the evidence of recent crustal 

 movements so commonly met with upon its margins, the great 

 irregularities of its depths, the proximity of vast axial uplifts of 

 late geological age, and the frequency of earthquake phenomena, 

 all indicate instability, and remind us strongly of similarly 

 constructed and disturbed regions within the area of the vast 

 Pacific. 



Let us now look at the Arctic and Antarctic coast-lines of 

 North America. From the extreme north down to the latitude 

 of New ^'ork the shores are obviously those of a partially sub- 

 merged region. They are of the same type as the coasts of 

 North-western Europe. We have every reason to believe 

 also that the depression of Greenland and North-east America, 

 from which these lands have only partially recovered, dates back 

 to a comparatively recent period. The fiords, and inlets, like 

 those of Europe, are merely half-drowned land valleys, and the 

 continental shelf is crossed by deep hollows which are evidently 

 only the seaward continuations of well-marked terrestrial features. 

 Such, for example, is the case with the valleys of the Hudson 

 and the St. Lawrence, the submerged portions of which can be fol- 

 lowed out to the edge of the continental plateau, which is notched 

 by them at depths of 474 and 622 fathoms respectively. There 

 is, in short, a broad resemblance between the coasts of the entire 

 Arctic and North Atlantic regions down to the latitudes already 

 mentioned. Everywhere they are irregular and fringed with 

 islands in less or greater abundance — highly denuded and deeply 

 incised plateaus being penetrated by fiords, while low-lying and 

 undulating lands that shelve gently seaward are invaded by 

 shallow bays and inlets. Comparing the American with the 

 opposite European coasts, one cannot help being struck with 

 certain other resemblances. Thus Hudson Bay at once suggests 

 the Baltic, and the Gulf of Mexico, with the Caribbean Sea, 

 recall the Mediterranean. But the geological structure of the 

 coast-lands of Greenland and North America betrays a much 

 closer resemblance between these and the opposite shores of 

 Europe than appears on a glance at the map. There is some- 

 thing more than a mere superficial similarity. In eastern North 

 America and Greenland, just as in Western Europe, no grand 

 mountain uplifts have taken place for a prodigious time. The 

 latest great upheavals, which were accompanied by much folding 

 and flexing of strata, are those of the Appalachian chain and of 

 the coastal ranges extending through New England, Nova Scotia, 

 and Newfoundland, all of which are of Paleozoic ^e. Con- 

 siderable crustal movements aff"ected the American coast-lands 

 in Mesozoic times, and during these uplifts the strata suflfered 

 fracture and displacement, but were subjected to comparatively 

 little folding. Again, along the maritime borders of North-east 

 America, as in the corresponding coast-lands of Europe, igneous 

 action, more or less abundant in Palaeozoic and early Mesozoic 

 times, has since been quiescent. From the mouth of the Hudson 

 to the Straits of Florida the coast-lands are composed of Ter- 

 tiary and Quaternary deposits. This shows that the land has 



