Jack the Young Canoeman: An Eastern Boy's Voyage in a Chinook Canoe

by George Bird Grinnell

Many questions suggested themselves to Jack during the climb. But the noise of the fall was so great that it was impossible to hear conversation, and it was not until they had reached camp that he was able to try to inform himself in regard to any of the matters about which he had wished to ask.

That night as they sat around the fire after dinner, he said to Fannin and Hugh: "I want to know how these big arms of the sea came to be formed. Why is it that every little way here we find an immense cañon running away back into the mountains, and the sea ebbing and flowing in it? Of course there's some reason for it. I don't understand what it is, but somebody must know."

Hugh smoked in silence for a few moments, and then, taking his pipe from his mouth and clearing his throat, said: "Yes, somebody must know, of course, and I expect to them that does know, it's mighty simple. I expect likely your uncle, Mr. Sturgis, knows about all these things, but I don't. I've got an idea from what I've heard him say, and from what I've seen up in the northern countries, that these big cañons were cut out by glaciers,—these big masses of ice, very heavy, and moving along all the time. It's easy for any one who has ever been around a glacier to see something of the terrible power that such a mass of ice has, and to see how it cuts and grinds away the surface of the earth and rock that it passes over. You've heard, and I've heard your uncle talk about these here cañons on the coast of Norway, that, from his tell, seem about just like these that we are travelling up and down, except that maybe these are bigger. We can all understand that if a very big glacier got running in a certain course, and kept running for thousands and thousands of years, it would cut out in the surface of the mountains a deep, narrow groove that might be like these cañons; but as I say, I don't know anything about them. I'm just guessing from what I've heard say."

"Well," said Fannin, "I don't know much about them either, but judging from what I've read, you're about on the right track. The books I've read say that there was a time, a good way back, when the whole of the northern part of North America was covered with a big sheet of ice, thousands of feet thick. That is what was called the glacial period, or ice age. This ice, if I understand it, was thicker towards the north—where it was piling up all the time, and getting still thicker—than it was toward the south, where the climate was milder, and where it was melting all the time. Now, although ice seems to us, who perhaps don't know much about it, about as firm and solid as anything can be, yet really it is not so. Learned men have made lots of experiments, which show that ice will change its form; and we all know that these glaciers that we see here are moving all the time, and, what's more, that they are moving faster in the middle than they are at the sides, where they rub against the mountains; in other words, where there is friction. That shows that ice is plastic, somewhat we'll say like molasses in January. It will flow, but it flows very slowly, and to make it flow at all the pressure on it may have to be very great. In other words, there's got to be a great force behind it, pushing it. Now the books say, that in the time of the ice age the sheet of ice that covered the country, being thick toward the north and thin toward the south, was constantly moving slowly from north to south; and I think the men that have studied them have seen in the scratches that the ice sheet made on the rocks and in the gravel and boulders and so on, that it carried along with it from one place to another strong evidence of this motion. Then, after a while, as I understand it, the weather got warmer, the ice sheet kept melting faster and faster from the south toward the north, and gradually the land got bare of ice. Of course it melted first on the lower lands, and last on the hills and mountains and peaks. It melted very slowly, and as it melted it left behind it on the mountains and in sheltered places where it was coldest, masses of ice which continued to flow along as ice streams, long after the general ice sheet had disappeared. These masses that were left did not move from north to south, because they were no longer being pushed in that direction. They just flowed down hill.

"If I understand it, there is only one place now in the world, in the North at least, that is covered by an ice sheet, and that's Greenland. But in the Northern mountains there are still a lot of remnants of the old ice sheet, and it is these remnants, I think, only thousands of times more powerful than they are now, that cut out these inlets that we are travelling over.

"We think that these are mighty deep, and so they are; but maybe you don't recognize how much depth there is below the water. Sometimes these inlets are sixty or eighty fathoms deep. There's from three hundred and fifty to five hundred feet from the surface of the water to the bottom of the Inlet, and nobody knows how deep the mud may be there before you could reach the bed-rock below it."

"I am very glad to know this," said Jack. "Most of it I have heard before; it sounds pretty familiar, but I never before heard it in such a connected way, and I never understood just what it meant. It seems to me pretty clear now, all except one point that I want to ask about. We all know how easily ice slips down over any surface, and there doesn't seem to be much friction. Now I can't understand just how the ice should cut out such a groove in the earth in any length of time, however long it might be. How is that? Can you explain it to me?"

For a little while Fannin sat thoughtfully staring into the fire, and then he replied: "Well, I think I understand it myself, and I think I can make you understand it as I do, but of course I do not guarantee that I am right about it. I only give you my idea.

"Suppose you take a piece of pine board and tilt it up and brace it to represent the side of your mountain. Then suppose you take a strip of paper, two inches wide, and we'll say of an indefinite length, because you've got to draw that paper down over that board, for say a thousand years, and never let it stop; for the glacier never stops, it is always being renewed at its head, and keeps on pushing down the mountain sides, just as a brook does that starts from a spring on a hilltop. Now, you might draw that paper down over that board for a thousand years, if you lived so long, and you would never wear much of a groove in the board. If you did wear one, it would be awful slow work. But now suppose, in the place of that strip of paper, you have a strip of sandpaper, just as wide, and just as long, and keep drawing that down for a thousand years, you can see that long before your thousand years were over you would have cut a big groove in the board, and in time, of course, you'd cut through the board. That, according to my understanding, is the way that the glacier acts. It isn't the ice by itself that cuts out the groove, but the ice is constantly picking up and rolling along under it fragments of rock and pebbles, and sand, and grinding these hard substances against the hard rock that makes up the faces of the mountains. So it is sawing down into the mountains all the time.