In imagination the geologist is present at the birth of whole mountain-ranges.  He sees them gestating in the womb of their mother, the sea.  Where our great Appalachian range now stands, he sees, in the great interior sea of Palaeozoic time, what he calls a “geosyncline,” a vast trough, or cradle, being slowly filled with sediment brought down by the rivers from the adjoining shores.  These sediments accumulate to the enormous depth of twenty-five thousand feet, and harden into rock.  Then in the course of time they are squeezed together and forced up by the contraction of the earth’s crust, and thus the Appalachians are born.  When Mother Earth takes a new hitch in her belt, her rocky garment takes on new wrinkles.  Just why the earth’s crust should wrinkle along lines of rock of such enormous thickness is not a little puzzling.  But we are told it is because this heavy mass of sediment presses the sea-bottom down till the rocks are fused by the internal heat of the earth and thus a line of weakness is established.  In any case the earth’s forces act as a whole, and the earth’s crust at the thickest points is so comparatively thin—­probably not much more than a heavy sheet of cardboard over a six-inch globe—­that these forces seem to go their own way regardless of such minor differences.

The Alps and the Himalayas, much younger than our Appalachians, were also begotten and nursed in the cradle of a vast geosyncline in the Tertiary seas.  We speak of the birth of a mountain-range in terms of a common human occurrence, or as if it were an event that might be witnessed, measurable in human years or days, whereas it is an event measurable only in geologic periods, and geologic periods are marked off only on the dial-face of eternity.  The old Hebrew writer gave but a faint image of it when he said that with the Lord a thousand years are as one day; it is hardly one hour of the slow beat of that clock whose hours mark the periods of the earth’s development.

The whole long period during which the race of man has been rushing about, tickling and scratching and gashing the surface of the globe, would make but a small fraction of one of the days that make up the periods with which the geologist deals.  And the span of human life, how it dwindles to a point in the face of the records of the rocks!  Doubtless the birth of some of the mountain-systems of the globe is still going on, and we suspect it not; an elevation of one foot in a century would lift up the Sierra or the Rocky Mountains in a comparatively short geologic period.

II

It was the geologist that emboldened Tennyson to sing,—­

    “The hills are shadows and they flow
       From form to form and nothing stands,
       They melt like mists, the solid lands,
     Like clouds they shape themselves and go.”

But some hills flow much faster than others.  Hills made up of the latest or newest formations seem to take to themselves wings the fastest.