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On the western side of the continent a narrow land occupied the site of the Sierra Nevada Mountains. Thus, even at the beginning of the Paleozoic, the continental plateau of North America had already been left by crustal movements in relief above the abysses of the great oceans on either side. The mediterraneans which lay upon it were shallow, as their sediments prove.

And here, as in other cases, man now is not content to be an impassive spectator and to be entirely controlled by his surroundings. He does not allow the "crustal relief" to have the upper hand in the matter. He will not admit that all he has to do is to adapt himself to his surroundings. That servile view of our position in the Universe is fast departing. We are determined to have the ascendancy.

The earth cools and contracts with almost infinite slowness, and the great crustal changes that take place go on, for the most part, so quietly and gently that we should not suspect them were we present on the spot, and long generations would not suspect them.

This rock may be made by the consolidation of volcanic cinders, of angular waste at the foot of cliffs, or of fragments of coral torn by the waves from coral reefs, as well as of strata crushed by crustal movements. FAULT SCARPS. A fault of recent date may be marked at surface by a scarp, because the face of the upthrown block has not yet been worn to the level of the downthrow side.

As on the Moon, the water came mostly from gypsum rock or occasionally from soil frost, both found on nearby crustal asteroids. Beyond the refineries bulged the domes of the city itself, housing factories, gardens, recreation centers, and sections that got considerably lost and divergent trying to imitate the apartment house areas of Earth. Frank Nelsen's wonder was hurried and dulled.

Third, along the western side of each continent recent crustal movements supplemented by volcanic action on a magnificent scale have given rise to a complex series of younger mountains, the two great cordilleras.

At each side of this chasm the two continents, the Old World and the New, would be left floating on their molten ocean; and some have even seen a confirmation of this in the lines of crustal weakness which we trace, by volcanoes and earthquakes, on either side of the Pacific.

It is not too much to say that the character and thickness of each formation of the stratified rocks depend primarily on these crustal movements. Along the Baltic coast of Sweden, bench marks show that the sea is withdrawing from the land at a rate which at the north amounts to between three and four feet per century; Towards the south the rate decreases.

As we decipher the records of the rocks in historical geology we shall see more fully how, in all the past, volcanic action has characterized the periods of great crustal movements, and how it has been absent when and where the earth's crust has remained comparatively at rest.

Under the resistless pressure of crustal movements almost any rocks, sandstones, shales, lavas of all kinds, granites, diorites, and gabbros may be metamorphosed into schists by crushing and shearing. Limestones, however, are metamorphosed by pressure into marble, the grains of carbonate of lime recrystallizing freely to interlocking crystals of calcite.