. Discovery. Science. Fig. 2.—the " PRESSING OUT " OF AX OROGENE TROUGH. the lands (see above) will be accentuated. As pressure continues other ridges form on the floors of the trough, parallel to the original bulge and extending outwards on either side from it. If there are any harder lumps in the floor they will serve first as occasions and then. as the cores of the growing folds (as a dead camel may cause a sand-hill). The blocks press in, the ridges press outwards. Pressure intensifies: the ridges jostle, mount up, push over one another, press some up and out, others in and down,
. Discovery. Science. Fig. 2.—the " PRESSING OUT " OF AX OROGENE TROUGH. the lands (see above) will be accentuated. As pressure continues other ridges form on the floors of the trough, parallel to the original bulge and extending outwards on either side from it. If there are any harder lumps in the floor they will serve first as occasions and then. as the cores of the growing folds (as a dead camel may cause a sand-hill). The blocks press in, the ridges press outwards. Pressure intensifies: the ridges jostle, mount up, push over one another, press some up and out, others in and down, in the search for room and still more room. The deeper and more compressed Orogene^ Zone ! Fig. 3.—diagram to show movements IN" OROGENE ZONE. parts are more plastic and serve as gliding planes for the more refractory materials above. The trough is now truly an orogenic zone, a zone giving birth to mountains. Ridge mounts on ridge, and above the shallowing out-flooding seas rise peaks, island rows, island chains, archipelagoes. Then up the inclined planes formed by the continental margins on either side press the ridges, layer thrusting over layer, advancmg against the solid land like great frozen waves, their steepest " breaking " faces always in front (outwards). Last of all the whole system is pressed up high and dry : the geosyncline is " pressed out " ; it is one-third of its original breadth ; it has become a zone of mountains. (Figs. 2-6.) These mountain zones are eloquent of their origin. Their materials reveal their birthplaces—the shallow, deep, or abysmal seas or the deeper rock zones under- lying these. Their structure, infinitely complicated by reason of their history, can generally be imravelled, and this structure is most striking. Every orogene zone is two-faced. It is as though two giant armies had advanced, back to back, each against an onpressing continent, and each had been frozen where it stood. In the front line are the tall
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