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Nature's Miracles: Familiar Talks on Science, Vol. 1.

<h2>CHAPTER XXVIII.</h2> <h3>SOME EFFECTS OF THE GLACIAL PERIOD.</h3> There is a wonderfully interesting effect produced by the action of water during the subsidence of a glacier at Lucerne, Switzerland. Some years ago there was discovered under a pile of glacial drift at the edge of the town of Lucerne a number of deep holes worn in a great ledge of rocks that crop out at that point. One of these pot-holes having been discovered, excavations were continued until a large number of them were unearthed of various shapes and sizes. I had the pleasure of inspecting some of them in the year 1881. They are situated within an inclosure called the Garden of the Glaciers. Some of these holes are twenty to thirty feet in diameter, and the same depth. There are others that are smaller in size, but all of them possess the same general characteristics. In the bottom of each one was found a bowlder, and in one or two cases two of them. The action of the water had given these bowlders a gyratory motion, which gradually wore away the rock underneath until round holes were formed to the size and depth heretofore mentioned. Where there was only a single bowlder the holes were almost perfectly round, but where there was more than one bowlder the holes were sometimes in an oblong shape. The bowlders were worn down to a very small size in most cases, and were round and smooth. The probabilities are that when the action first began these bowlders were large and of irregular shape. They must have been, in order to do the enormous amount of grinding that some of them did to produce excavations in the solid rock with a diameter of thirty feet and a depth about the same. The bottoms were round like an old-fashioned pot, and the insides polished perfectly smooth. This was purely an effect of the tumbling about of the bowlders by the running water from the melting ice of the great glacier that covered that region some time in the long ago. There are other effects produced in rocks during the ice flow in North America that are very interesting. Great grooves are formed in the rocks, in many cases running for long distances, that have been worn in by the cutting power of the great ice sheet during the progress of its movement. There is a great groove to be seen at Kelly's Island in Lake Erie. It will be remembered that this lake is supposed to have been formed entirely by the ice of the glacial period. In its movement across the country which is now covered by the lake the ice encountered a huge rock formation at Kelly's Island. Great V-shaped grooves were cut through this rock by the action of the ice, deep enough for a man to stand in. In other places the rock was planed off in the form of a great molding, a number of feet wide, with the same smoothness and accuracy as though done by a machine. Another effect of the glacial period has been the creation of numerous waterfalls throughout the glaciated area. The most notable instance is that of the Falls of Niagara. In preglacial times the beds of all rivers and water courses had worn down to an even slope, so that there were very few, if any, waterfalls such as we have to-day. As we have before stated, Niagara River as well as the St. Lawrence River is a new outlet for the drainage of the great lakes. A part of this drainage formerly had its outlet through the Mohawk Valley into the Hudson, which is now filled up with glacial drift. The evidence is so conclusive that it is no longer doubted that the Niagara River dates from the time that the ice receded from that point. When the water first began to flow through this new channel it plunged over the high rocky cliff at Queenstown, and from that time to this it has been wearing its way back to the present position of Niagara Falls, a distance of about seven miles. A vast amount of interest centers about this river because it is the best evidence we have of the time that has expired since the glacial period. A great deal of study has been given to determine the amount of erosion at the Falls during a year's time. If this could be accurately determined, then by measuring the distance from the present falls to Queenstown, we could easily determine the number of years since the ice period. It is difficult to determine, for the conditions may have changed; for instance, the rock at the Falls to-day is said to be harder than it is further down toward Queenstown. The estimates vary from 35,000 years to 10,000 years—that is, from a rate of erosion of five feet to one foot, per year. Every science is, nearly or remotely, related to every other science. If we could determine accurately the date of the ice period it would settle a whole lot of other questions that are related to it, and one of them is the antiquity of man. Many stone implements such as were made and used by the aborigines have been found at various times buried deeply under the glacial drift. These finds have occurred so often that there no longer remains a doubt but that a race of men existed on this continent in preglacial times. There are evidences that at a time long ago the temperate zone extended far north of this, and it is not impossible that what is now the continent of Asia and that of North America were joined. In fact, they come very close together to-day at Bering Strait. If such were the case this continent could have been inhabited from the old world by an overland route. This, however, is mere speculation. There are a number of factors that are taken into account in determining the period of the ice age besides the Niagara River and the Falls. The Falls of St. Anthony at Minneapolis (which like the Niagara is a creature of the ice age), the wear of water on the shores of the great lakes, the newness of the rocks that are piled up on the terminal moraines, all point to a much shorter period since the ice age than it used to be supposed, and indicate that the time does not exceed 10,000 years. To the ordinary mind the ice age no doubt seems like a myth, but to the man of science who has made a study of all of these evidences it is as real as any fact in history, and much more real than some of the history we read. In the former case we are dealing with evidences that appeal to our senses, while in the latter we are dealing with the recollections of men concerning what purport to have been actual transactions, and we know enough about the human mind to make it difficult sometimes to draw the line between the actual and the imaginary. The glacial period is not only closely related to the topography of North America and parts of Europe in the changing of river beds, the formation of lakes, the transportation of rock, the grinding down of mountains and spreading the débris over thousands of miles in extent, but it is related in an intimate way to many of the sciences, such as botany and zoölogy. A study of the flight of animals and plants in front of the great advancing ice sheet is a subject of intense interest. The migration of great forests would seem to be an impossible thing when viewed from the standpoint of a casual observer. It is true that individual trees could not take themselves up and move forward in advance of the oncoming ice, but they could and did send their children on ahead, and when the ice had overtaken the children there were still the children's children ad infinitum. By an examination of the map it will be seen that the land gathers about the north pole, while the south pole is surrounded chiefly by great oceans. As we have hinted before, in preglacial times the temperate zone extended much farther north than it does to-day, and north of that there was an arctic zone (which to-day is largely covered with ice sheets), where forests, plants, and animals flourished that were fitted for an arctic climate. When the glacial period set in and the ice sheet began its southern journey this zone or climate was moved southward in front of the ice, thus forming, as it were, a moving zone whose climatic conditions were similar to those of the arctic regions (at least so far as temperature was concerned) in preglacial times. The ice movement was so gradual that time was given for forests to spring up in advance of it that moved southward at about the same rate as that of the moving ice. Undoubtedly the average movement was very slow and was probably thousands of years reaching its southernmost limit, which is now marked by the terminal moraine. Thus it will be seen that while the individual trees and plants could not move, the forest as a whole could. It was gradually being cut down on its northern limit and as gradually it grew up on the southern limit of the zone; the ice movement being so slow that the young tree of to-day on the southern limit becomes a full-grown king of the forest by the time the relentless icebergs reach it and cut it down and thus the process went on until the plants, trees, and animals of the arctic region were driven hundreds of miles south of the great chain of lakes on the northern boundary of the United States. Many of the animals of preglacial times were unable to stand the strain of the ever-changing climatic conditions and have become extinct, but their fossil remains are left to tell the story to the present and future ages. Much of the history of those times is a sealed book, but the persevering energy of the glacialist and archæologist is gradually turning the leaves of this old book and revealing new chapters of the wonderful story of the ice. As the ice receded the arctic zone again traveled northward, and many animals, plants, and trees that had survived the vicissitudes of the ice age, traveled back with it. Some of them, however, became acclimated and by adapting themselves to the new conditions remained behind to live and grow with the aborigines of preglacial times. Some of the plants and flowers that grew in profusion immediately under the edge of the great ice sheet were unable to live under the new conditions of increased warmth—that came with the retrograde movement of the ice—and either had to follow closely the receding ice or escape to higher altitudes, where they found a congenial clime. Thus it is that we have arctic plants and flowers above the timber line and near the snow line of our high mountains. In proof of this theory it has been found that these arctic plants do not exist upon high mountains, such as the Peak of Teneriffe, where they have been isolated from the glaciated region. The Peak of Teneriffe is situated on one of the Canary Islands, surrounded by water, so that there was no possible chance for the arctic plants to seek refuge on these isolated elevations, such as the continental mountains furnish. Thus it will be seen that the progression and recession of the ice have not only formed great lakes, changed river beds, and covered a million square miles of area with glacial drift averaging fifty feet in depth, making many waterfalls and giving variety to the surface of the earth, besides producing the finest agricultural region in the world, but have also given variety to our forests and plants wherever this ice sheet has extended. <hr style="width: 65%;" /> <div style="break-after:column;"></div>

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