Moreover, we are staggered by the element of vast time that is implied in the history of development.  Were it not for the records in the rocks, we could not believe it at all.  All the grand movements and processes of nature are quite beyond our ken.  In the heavens only the astronomer with his prisms and telescopes traces them; only the geologist and palaeontologist read their history in the earth’s crust.  The soil we cultivate was once solid rock, but not in one lifetime, not in many lifetimes, do we see the transformation of the rocks into soil.  Nations may rise and fall, and the rocks they looked upon and the soil they tilled remain practically unchanged.  Geologists talk about the ancient continents that have passed away.  What an abyss of time such things open!  They talk about the birth of a mountain or the decay of a mountain as we talk of the birth and death of a man, but in doing so they reckon with periods of time for which we have no standards of measurement.  They walk and talk with the Eternal.  To us the mountains seem as fixed as the stars.  But the stars, too, are flitting.  Look at Orion some millions of years hence, and he will have been torn limb from limb.  The combination of stars that forms that striking constellation and all other constellations is temporary as the grouping of the clouds.  The rise of man from the lower orders implies a scale of time almost as great.  It is unintelligible to us because it belongs to a category of facts that transcends our experience and the experience of the race as the interstellar spaces transcend our earthly measurements.

We now gaze upon the order below us across an impassable gulf, but that gulf we have crossed and without any supernatural means of transportation.  We may say it has been bridged or filled with the humble ancestral forms that carried forward the precious evolutionary impulse of the vertebrate series till it culminated in man.  All vestiges of that living bridge are now gone, and the legend of our crossing seems like a dream or a miracle.  Biological evolution has gone hand in hand with geological evolution, and both are on a scale of time of which our hour-glass of the centuries gives us but a faint hint.  Our notions of time are not formed on the pattern of the cosmic processes, or the geologic processes, or the evolutionary processes; they are formed on the pattern of our own brief span of life.  In a few cases in the familiar life about us we see the evolutionary process abridged, and transformations like those of unrecorded time take place before our eyes, as when the tadpole becomes the frog or the grub becomes the butterfly.  These rapid changes are analogous to those which in the depths of geologic time have evolved the bird from the fish or the reptile, or the seal and the manatee from a fourfooted land animal.  Our common bluebird has long been recognized as a descendant of the thrush family; this origin is evident in the speckled breast of the young birds and in the voices of the mature birds.  I have heard a bluebird with an unmistakable thrush note.  The transformation has doubtless been so slow that an analogous change taking place in any of the bird forms of our own time would entirely escape observation.  The bluebird may have been as long in getting his blue coat as man has been in getting his upright position.