Unexplored! Part 16

"Either that or volcanic lava."

"But how did it----"

"Just a minute. Of course land ma.s.ses have gone down as well as up, but the general trend has been decidedly upward, while the trend of the ocean floor has been downward. At that, the sh.e.l.l of the earth--so to speak--is only about 150 miles thick or a fiftieth of the earth's present diameter."

"Then I should think the oceans would be growing deeper," ventured Pedro.

"Right again. When this earth reaches its old age,--speaking in terms of centuries,--it will likely be all ocean. And there used to be far more land, in proportion, than there is now. There was less ocean water then because of all that is continually pouring through hot springs.

"Of course the land is slowly being washed back into the ocean. And the higher the mountains, the steeper the stream beds, and hence the faster the streams, and the faster they erode the high elevations, till finally all is reduced to sea level again."

"Then how do the mountains get rebuilt?" Pedro testified his interest.

"The earth has, as I think I said before, shrunk between 200 and 400 miles in diameter,--since the beginning,--'when the earth was unformed and void, and darkness was upon the face of the deep.' It is still shrinking. And this internal movement is felt on the surface in differences that generally amount to only a few hundred feet. I can show you places over there on the East wall of the Sierras where the mountains have been upthrust that way.

"Then, every now and again, the interior activities fairly break the rocky earth sh.e.l.l or lithosphere, and whole mountain ranges are raised.

There have been at least eight such minor breaks in the earth crust in North America alone, and each time ranges perhaps a thousand miles long, or more, have been raised near one end of the continent or the other. In addition, there have been major readjustments that thrust whole continents higher and ocean beds lower. Geologists find evidence of at least six of these major breaks in the earth crust,--marking the beginnings of the Archeozoic Era, when _life_ originated, the Proterozoic Era, or age of _invertebrates_, the Paleozoic Era or age of _fish_ dominance, the Mesozoic Era or age of _reptile_ dominance, the Cenozoic Era or age of _mammal_ dominance, and the present Psychozoic Era or age of _man_."

"Phew!" whistled Long Lester again. "Don't tell me this earth used to be all fish."

"It did, though. We'll go into that some other time. I'll just finish about continent building now, and then we'll turn in. At these times when the lands are at their highest and the oceans are smallest in breadth, (because greatest in depth), the continents are united by land-bridges such as those we have now uniting North and South America."

"And Alaska and Asia?" suggested Ted.

"Practically, yes. And probably, at one time, South America and Australia. These land-bridges changed the direction of the ocean streams. You know in the age of reptiles there was nothing to divide the Atlantic from the Pacific. Added to that, the high mountain ranges took the moisture out of the winds from the oceans, as the Rockies now do the Pacific trade winds, so that by the time they reach Nevada there is no moisture left in them to form clouds and fall in rain, and we have desert.

"Of course the animals that lived on the earth in its flatter, more temperate stage now have to adapt themselves to life on high, cold elevations, or in dry, hot desert areas, or to migrate via the land-bridges to more favorable climates. Those unable to do this perished.

"For instance, take the age of reptile dominance, (the Mesozoic Era), which was in turn divided into four periods, those of dinosaurs, (the Tria.s.sic period, a rock from which I showed you, if you remember), the Jura.s.sic period, which gave rise to flying reptiles, from which our first birds were derived; the Comanchean period, which gave rise to flowering plants and the higher insects, and the Cretaceous period, when our most primitive mammal forms evolved.

"At first the earth was peopled with dinosaurs and flying dragons, and the seas by squid-like mollusks. In those days all the earth was level, swampy, tropic and overgrown with giant tree ferns and a primitive conifer.

"As the high mountain ranges arose and deserts were made, these forms gradually gave way to flowers and hardwood forests, peopled with insects and mammals. Only the most intelligent forms survived, and the struggle itself developed a higher degree of intelligence."

"What in tarnation were _dinosaurs_?" asked Long Lester.

"Oh, haven't you ever seen pictures of them?" laughed Ace. "Picture a giant lizard, perhaps 40 feet long----"

"Here, here," protested the old man. "I don't bite."

"It is perfectly true," said Norris soberly.

"Honest Injun!" vowed Ace. "One of these fellows was a sort of cross between a crocodile and a kangaroo, what with his long hind legs that he could walk half erect on. There were some as small as eight or ten inches, too, and some so large that you wouldn't have come to his knee.

His big toe was as long as your arm."

"And how do you know all that?" protested the old prospector feebly.

"By their bones,--fossils. Why, there have been fossil bones of a dinosaur found right in the Connecticut Valley! There was one found a hundred years ago in Oxford, England. We have heaps of fossils of them out West here. In fact, this part of the world used to be their stamping ground, though fossils of them have been found as far away as New Zealand."

"Did they eat people?" gasped Lester.

"There weren't any people in those days to eat, but some of them preyed on other animals, and some browsed on the herbage of the swamps. They didn't have much of any brains, the Triceratops, dinosaurs twice as heavy as elephants, that looked like horned toads, didn't have two pounds of brains apiece, or so we infer from the size of their skulls. They knew just about enough to eat when they were hungry, and not enough to migrate when things got unlivable for them, and so they perished off the face of the earth."

"I'm sh.o.r.e glad of that," the old man heaved a sigh of relief. "I'd sh.o.r.e hate to 've met up with one of them fellows."

"And next time I want to cast aspersions on any one's intelligence,"

shouted Pedro, "I'm going to call him a--what was it?"

"_Triceratops_," said Norris. "Some dinosaurs,--in fact, most of them,--lived in the swamps, and had long, snakelike necks and flat, apparently earless heads, and long tails. But Triceratops had a three-horned face, one horn over each eye to protect it in battle and one over the nose. Of course he was the largest animal of his time, but he probably fought rival swains for his lady love. We have a pair of Triceratops horns in the National Museum. One is broken, and it must have been broken during life, for the stump is healed over. There were many other kinds of dinosaurs. If we come to any fossil remains, I'll tell you more about them. But," (stifling a yawn), "I guess you fellows have had about all you can stand for to-night."

The boys protested to the contrary, but Norris promised the rest of the story their next evening together around a bon-fire.

In the middle of the night the boys were awakened by a terrific racket.

Long Lester was yelling for all he was worth. Every one started wide awake, and Norris threw a handful of browse on the fire to light the scene. Then the old man managed to articulate: "Gosh A'mighty!--I sure thought the Dinosaurs were arter me!"

"You've been dreaming," Norris laughed, while the boys fairly rolled over one another in their enjoyment.

Ace and Ted now made two flights daily in search of the Mexicans, or the smoke of their cook-fire.

Next day they came to a canyon that filled the Geological Survey man with profound enthusiasm, for, he said, it ill.u.s.trated both the last glacial period and the last period of volcanic mountain building. First they noted that the little mountain stream had worn its torrential way through the basalt or volcanic rock in a narrow canyon perhaps 200 feet deep. A flow of molten basalt, accompanied by cinders, had been erupted from the 8,000-foot peak at the upper end of the canyon, and had flowed down in a layer 200 feet thick when it hardened. It had flowed,--as the underlying rock still showed in places,--over a lateral moraine or rock debris left by a glacier as it flowed down that way. And from the weathered condition of this rock debris, Norris said, it must have been a glacier, not of the last ice age, but of the one preceding,--for of the four glacier periods generally recognized by geologists to-day, evidences of the last two can be seen in the Sierras.

What made this little canyon even more of a find, (from the point of view of what he wanted to show the boys), was that on top of the volcanic rock lay the deposit from another glacier, one that flowed in the last ice age, as the condition of the rock debris plainly showed the expert.

The boys tucked a few rock specimens into their packs and launched an avalanche of questions. But he made them wait till they had established all snug for the night beside a stretch of rapids, where they could look forward to catching trout for breakfast. Then, lighting his pipe, and stretching his feet to the bon-fire,--for the night wind swept cool upon them,--Norris began with Ted's question as to glaciers and volcanoes.

"During the times I spoke of last night, when the earth crust is breaking, the molten rock and gases and water vapor in the interior of the planet rise in the hearts of the mountain ranges, and often break through as active volcanoes, pouring their lava and ash over the underlying granite, and building it still higher.

"These heightened mountain ranges bring about the glacial climates. For the snows on their cold peaks do not melt when summer comes, and consequently they acc.u.mulate, and acc.u.mulate, till their own weight presses them down as hard as ice,--that is, makes glaciers of them. I am going to be on the look-out for a glacier, for you will have a good chance to see them in this region. At the same time, during these glacial periods, the astronomer could explain how it is that the temperature is from ten to twenty degrees colder in both winter and summer than it is now, so that helps the ice to acc.u.mulate. Then the glacier, flowing slowly, slowly, (a river of ice), down the mountainsides, carries with it quant.i.ties of the underlying rocks, till it reaches a lower level where the ice melts and it becomes a river and carries those rocks and soil to the sea. That way, the mountains are gradually worn down to sea level and the whole cycle is ready to start over again."

"I see," said the ranch boy. "How long ago did you say the last glacier period came?"

"Probably not since the time of the first men,--perhaps 30,000 years ago."

"And those glacial deposits you showed us to-day are 30,000 years old?"

the boy breathed.

"Yes, and the deposits from the glacial period before that are older still,--a souvenir from the age of reptile dominance."

"Then when did the other ice ages come? Did you say there were five?"

"I did, but only four great ones. There were two away back in the age of invertebrates."

"Then has the climate been the same since the last ice age?"

"Not at all. The change is gradual, and geologists naturally conclude that some time we will have another ice age. We'll hope man has found a better way to keep warm by that time. Our climate, with all its ups and downs, is little by little, through the centuries, growing colder!"

"And how do you know about all these ups and downs of climate?"

challenged Long Lester.