“The salt was originally in the rock of the earth’s crust,” Norris explained with a pleased smile at the old man’s interest. “As this igneous rock weathered with time, the rain and the streams washed it into the ocean. Then when the sea water evaporates––”
“To make clouds, to make more rain?” Long Lester recited.
“Yes,—the salt of course remained behind, so that the oceans have been growing constantly saltier since the earth began. Yet even now sea water must be nine-tenths evaporated before the sodium begins to precipitate, as we say.”
“So there is room for a lot more.”
“Especially as the oceans are growing larger all the time.”
“But doesn’t the ocean give it back to the land when it leaves these sediments along the shore?”
“Not to any extent, speaking comparatively. But one of the interesting things about the salt in the sea is this: Chemists and geologists estimate that, for the amount of salt in the sea, enough of the original earth crust must have been weathered away to have covered the continents over 6,000 feet high. And that calculation just about fits what we believe to have happened.
“The United States Geological Survey gave out an official statement in 1912 that this country is annually being washed back into the ocean at the rate of two hundred and seventy million tons of matter dissolved in the streams and five hundred and thirteen millions of tons of matter held in suspension in the same streams. That is to say, the oceans every year receive from the surface of the United States seven hundred and eighty-three millions of tons of rock materials.
“That means that, here in this part of the country at least, one hundred and seventy-seven tons per square mile are being washed back each year.”
“Gee!” said Ted. “I should think, at that rate, that the continents would have been all washed away long ago.”