STORY OF A STROLL IN THE RAIN
Another story found in museums is written in slate—not by a rain-drop but by a living creature. The slate shows the track of a reptile with feet like a bird. Evidently he was strolling along in the rain; for there you see the marks of the rain-drops right among the marks of his feet, and in the footprints themselves. Being a reptile who spent much of his time in or near the water he no doubt enjoyed these little pats of the rain-drops as he went along.
BUT THIS STROLL WAS TAKEN IN THE SUN
In another of these museum specimens we see written out just as plainly the story of a stroll in the sun. There are the imprints of Mr. Reptile's feet, and there are the sun-cracks in the mud showing that the sun was shining—or at least that it had been shining for several days or weeks, for it takes a little time to make sun-cracks in mud. This story, we might suppose, was written so that it could be read by the blind; the cracks, as well as the footprints, are brought out in raised lettering. Sun-cracked mud, after a long dry "spell," will bake so that the cracks will not be washed out by the returning tide but instead be filled by other material, and this material will go on building up to a certain extent; so making those ridges.
"THEN THERE CAME A LONG DRY SPELL"
This shows how the cracks in dried-up mud are preserved in stone. The process is the same as in the case of the stone imprints of rain-drops, the imprints being protected by successive deposits of mud by quiet tides, and afterward turning to stone.
THE STONE AUTOGRAPHS OF GENTLE BREEZES
On still other stones you will find written the story of gentle breezes that stirred the water and made ripples on long-buried shores. First the breezes rippled the shallow waters near the shore. Then the waters rippled the sand, and the sediments of the tide preserved these ripple marks as they did the rain-drops and the footprints.
But the wind alone, without the help of water ripples, can write its name in the sands of time. And when you get to know the handwriting of wind and wave you will not mistake the one for the other. You are likely to find wind ripples on any big heap of sand. Have a good look at them and then go down to shallow water on a sandy shore and compare the two kinds. That's the way the great men of science do; they notice every little thing.