Notices of Memoirs — Prof, LapivorWs Address. 473 



the crushing and crumpling of its rocks is the greatest. It is on the Atlantic side 

 of the eastern fold that the contortion and metamorphism of its rocks are at their 

 maximum, while in the common and gently sloping trough of both folds, namely, 

 in the intermediate Mississippi Valley, the entire geological sequence remains 

 practically unmodified throughout. 



Again, which of these two American folds should be the more active at the 

 present day ? Taught by our study of the mountain wave, the answer again is 

 immediate and conclusive. It must be that fold whose septum has the steeper 

 gradient. Geology and geography flash into combination. The steeper Pacific 

 septum of the western fold from Cape Horn almost to Alaska is ablaze with 

 volcanoes or creeping with earthquakes, while the gently inclined Atlantic septum 

 of the eastern fold from Greenland to Magellan Straits shows none, except on 

 the outer edge of the Antilles, in the very region where the slope of the 

 surface is the steepest. We see at a glance that the vigour of these two great 

 continental folds, like those of our mountain waves, varies directly as the surface 

 gradient of the septum. 



But the geographical surface of North America, considered as a whole, is in 

 reality that of a double arch with a sag or common trough in. the middle. We 

 have seen already that this double arch, must be regarded as the natural com- 

 plement of the equally double Atlantic trough. Here, then, if the path of analogy 

 we have hitherto so triumphantly followed up to this point is still to guide us, the 

 trough of the Atlantic must be, not only in appearance but in actuality, formed of 

 two long minor folds of the same grade as the two that form the framework of 

 America, but with their members arranged in reverse order. If so, their submarine 

 septa ought also to be lines of movement and of volcanic action. And this is 

 again the case. The volcanic islands of the Azores and St. Helena lie not exactly 

 on the longitudinal crests of the mid-oceanic Challenger ridge, but upon its 

 bounding flanks. 



But we have not yet, however, finished with our simple folds. If we draw a 

 line completely round the globe, crossing the Atlantic trough at its shallowest, 

 between Cape Verde and Cape St. Roque, and continued in the direction of 

 Japan, where the Pacific is at its deepest, we find that we have before us a 

 crust fold of the very grandest order. We have one mighty continental arch 

 stretching from Japan to Chili, broken submedially by the sag of the Atlantic 

 trough ; and we see that this great terrestrial arch stands directly opposed to 

 its natural complement, the great trough of the Pacific, which is bent up in the 

 middle by the mightiest of all the submarine buckles of the earth-crust, on which 

 stand the oceanic islands of the central Pacific. 



But if this be true, then the septum of all septa on our present earth-crust 

 must cross our grandest earth fold where the very steepest gradient occurs along 

 this line, and it must constitute the centre-point of the moving earth fold, and of 

 greatest present volcanic activity. And where is this most sudden of all de- 

 pression? Taught once more by our geological fold, the answer is instantaneous 

 and incontrovertible. It is on the shores of Japan, the mightiest and most active 

 of all the living and moving volcanic localities on the face of our globe. 



But the course of the line which we indicated as forming our grandest terres- 

 trial folds returns upon itself It is an endless fold, an endless band, the common 

 possession of two sciences. It is geological in origin, geographical in effect. It 

 is the wedding-ring of geology and geography, uniting them at once and for ever 

 in indissoluble union. 



Such an endless fold again must have an endless septum, which, in the nature 

 of things, must cross it twice. Need I point out to the merest tyro in these 

 wedded sciences that if we unite the Old and New Worlds and Australia, with 

 their intermediate sags of the Atlantic and Indian Oceans, as one imperial earth 

 arch, and regard the unbroken watery expanse of the Pacific as its complementary 

 depression, then the circular coastal band of contrary surface flexure between 

 them should constitute the moving master septum of the earth's crust. This 

 is the "Volcanic Girdle of the Pacific," our "Terrestrial Ring of Fire." 



Or, finally, if we rather regard the compact arch of the Old World itself as 

 the natural complement of the bi^oken Indo- Pacific depression, then the most 

 active and continuous septal band of the present day should divide them. Again 

 our law asserts itself triumphantly. It is the great volcanic and earthquake band 



