700 REPOET— 1892. 



sink to the profoundest depths. This complementary relationship descends even to 

 the minor features of the two. Where the great continental sag sinks below 

 the ocean level, we have our gulfs and our Mediterraneans, seen in our type 

 continent as the Mexican Gulf and Hudson Bay. Where the central oceanic 

 huckle attains the water-line we have our oceanic islands, seen in our type ocean 

 as St. Helena and the Azores. Although the apparent crust-waves are neither 

 equal in size nor symmetrical in form, this complementary relationship between 

 them is always discernible. The broad Pacific depression seems to answer to the 

 broad elevation of the Old World — the narrow trough of the Atlantic to the 

 narrow continent of America. 



Every primary wave of the earth's surface, again, is broken up into minor weaves, 

 in each of which the ridge and its complementary trough are always recognisable. 

 The compound ridge of the Alps answers to the compound Mediterranean trough ; 

 the continuous western mountain chains of the Americas to the continuous hollow 

 of the Eastern Pacific which bounds them ; the sweep of the crest of the Himalaya 

 to the curve of the Indo-Gangetic depression. Even where the surface vraves of 

 the lithosphere lie more or less buried beneath the waters of the ocean and the 

 seas, the same rule always obtains. The island chains of the Antilles answer to 

 the several Caribbean abysses, those of the ^Egeau Archipelago answer to the 

 Levantine deeps. 



Draw a section of the surface of the lithosphere along a great circle in any 

 direction, the rule remains always the same : crest and trough, height and hollow, 

 succeed each other in endless sequence, of every gradation of size, of every degree of 

 complexity. Sometimes the ridges are continental, like those of the Americas ; some- 

 times orographic, like those of the Himalaya; sometimes they are local, like those 

 of the English Weald. But so long as we do not descend to minor details we find 

 that every line drawn across the earth's surface at the present day rises and falls 

 like the imaginary line drawn across the surface of the waves of the ocean. No 

 rise of that line occurs without its complementary depression ; the two always go 

 together, and must of necessity be considered together. Each pair constitutes one 

 of those geographical units of form of which every continuous direct line carried 

 over the surface of the lithosphere of our globe is made up. This unit is always 

 made up of an arch-like rise and a trough-like depression, which shade into each 

 other along a middle line of contrary curvature. It resembles the letter S or 

 Hogarth's line of beauty, and is clearly similar in form to the typical wave of 

 the physicist. Here, then, we reach a very simple and natural conclusion : viz., 

 the surface of the earth-crust of the present day resembles that of a series of crust- 

 waves of different lengths and different amplitudes, more or less irregular and 

 complex, it is true, but everywhere alternately rising and falling in symmetrical 

 halves like the waves of the sea. 



Now this rolling wave-like earth-surface is formed of the outcropping edges of 

 the rock formations which are the special objects of study of the stratigraphical 

 geologist. If, therefore, the physiognomy of the face of our globe is any real index 

 of the character of the personality of the earth-crust beneath, these collective 

 geographical features should be precisely those which answer to the collective 

 structural characters of the geological formations. 



In the earlier days of geology one of the first points recogni,«ed by our strati- 

 graphists was the fact that the formations were successive lithological sheets, who.se 

 truncated outcropping edges formed the present surface of the land, and that these 

 sheets lay inclined at an ano-le one over the other, or, as William Smith quaintly 

 expressed it, like a tilted ' pile of slices of bread-and-butter.' But as discovery 

 progressed, the explanation of this arrangement soon became evident. The forma- 

 tions revealed themselves as a series of what had originally been deposited as hori- 

 zontal sheets, lying in regular order one over the other, but which had been 

 subsequently bent up into alternating arches and troughs (the anticlines and syn- 

 clines of the geologist). Their visible parts, which now constitute the surface of 

 our habitable lands, are simply those parts of the formations which are cut by the 

 irregular plane of the present earth surface. All those parts of the great arches 

 and troughs, formerly occurring above that plane, have been removed by denu- 



