CONTENTS. Volcanic indications in mountain chains. General character of a mountain range. crushing. Crushing, the effect of gravitation on the rigid crust of a shrinking earth. Metamorphism. Mountain formation a gradual process. Cause of the earth's shrinking. Conduction of heat. Recapitulation. The earth constantly decreasing in size. Upheaval and depression the effects of xi The agents of denudation. Formation of glaciers. The great Sources of river supply. The Mahánadi. Distinction of the collecting and distributing areas. The catchment basin and delta. Forms of valleys. The course of a river; by what causes determined. The watershed of the Mahanadi. Area of the basin. Its rainfall; how disposed of. Freshets and floods. Great floods of the Mahanadi. Dry weather drainage; its source. Surface springs. The importance of forests and disastrous effects of their destruction. The delta ; its channels. Cause of their overflow and formation of alluvium. Effects of embanking. Flooding of deltas. His- The Indus, and its sources of supply. Its fluctuations. floods. Their causes. Erosion of valleys by glaciers and rivers. Forms of valleys. Decomposition of rocks. Land- slips. Detritus. Gravel formations of Guge and Ladakh. Alluvial plains. Waterfalls of India. Salt Lakes. Their origin. Fresh-water lakes. Lagoons. Chilka and Púlicat Present distribution of the land, the result of geological changes. Unequal distribution in the two hemispheres. Antiquity of the continents and their changes of form. General structure of the existing continents. Europe. Asia. its mountain chains, table lands, plains and peninsulas, and their relative antiquity. Inland seas. The rainfall and winds of Asia. Causes of the deserts. Rivers of Asia. Causes of variation in the vegetation. Tropical vegetation. That of the Eastern Himalaya, &c. That of the plains. Useful crops of India. Temperate and Alpine vegetation of the Himalaya. Its poverty in Tibet. Vegetation of Persia and Western Asia. General laws of vegetable distribution. Illustrations of the distribution of animals. Continental and oceanic PHYSICAL GEOGRAPHY. INTRODUCTION. WHAT PHYSICAL GEOGRAPHY IS ABOUT, AND HOW TO LEARN IT. BEFORE we enter systematically on the study of Physical Geography, let us try to gain a general idea of the kind of knowledge to which this name is applied. To do so we will take a scene that must be familiar to many of those whom I address. After some rainy morning in July or August, I will suppose you to take your stand on the bank of the river that flows by your village, and, perhaps, in mere listlessness, watch the turbid flood swirling past. The chur opposite, which the river left dry when its waters fell at the close of the last rainy season, and which till lately was covered by a rich green crop of Indigo or bright yellow mustard, is now more than half cut away and buried beneath the waters; and the steep bank which the stream has cut along the part not yet submerged is rapidly giving way, and masses, many times larger than the house you live in, from time to time detach themselves, and falling, are swallowed up by the deep muddy stream. Has it ever occurred to you to ask yourself why these things are as you see them? You have probably witnessed the same kind of thing scores of B.G. $ B PHYSICAL GEOGRAPHY. times, and you may perhaps think that there is nothing very interesting in this swelling and shrinking of the river, in its heaping up churs and again destroying them, in the waters hurrying on always in one direction and never returning on their course. You know that the same thing is repeated year after year, and expect that if you live fifty years and come back to the spot you now stand on, the scene before you will be just the same as that which you gaze on to-day. But now consider a little. On thinking the matter over, you may recall to mind, that the chur that is now so rapidly disappearing before your eyes was not in exactly the same place, nor was it so large as that which, in a certain sense, it replaced, and which you remember two years ago. Moreover, that the stream, which, during the cold-weather months, separated it from the bank you stand on, was, during this last season, deeper than that which flowed between them in the cold weather of the year before; and if you ask the old people of the village, they will, perhaps, tell you that, thirty or forty years ago, the river itself was a moderate-sized khall; and that the old river channel, seven or eight miles off, which is now little more than a string of pools, was at that time a well-filled river, which could scarce be crossed without a boat even in the dry weather. Such things happen constantly in Bengal. Perhaps this may have aroused your curiosity, and you begin to enquire of people who have come from other parts of the country, whether they have known such changes elsewhere. Among others, you question some one who for many years lived in the Maimansing, Dacca or Bograh District, and you learn from him that it is well known to the people of those districts, that, about sixty or seventy years ago, the Brahmaputra, which up to that time had flowed past Maimansing and a long way to the east of Dacca and of the high Mádhapúr jungle to the north of it, changed its course, and has ever since flowed to the west of the Mádhapúr jungle, and a long way west of Dacca, joining the Ganges at Goalundo, where the railway now terminates. Some one else-it may be from Rangpúr-tells you that, at a some what earlier date, the Tísta, a large river from the Himalaya, which used to flow southwards into the Ganges at Jaffirganj, in 1787 suddenly changed its course and opened out a new channel to the eastward; in which it has since flowed, joining the Brahmaputra above Divánganj. These are not mere vague traditions; they are well established historical events. Old maps exist, which were drawn before these changes took place, and they show that these rivers then flowed as I have told you. So you see that the changes which you may have noticed yourself in the stream at your feet, or which have been witnessed by persons whom you see daily, are but small examples of much greater permanent changes which a little enquiry will enable you to learn about. But we have a great deal more to learn from the river before you. You can see that the water is very muddy; before it is fit to drink, you must let it stand for some time. Fill a clean pot with this muddy water, and let it stand undisturbed. In the course of a few hours, you will find a layer of earthy matter at the bottom of the pot, very much like the loam of the fields around, but the water must stand for several days before it is quite clear, and then you will find a thin layer of very fine mud or clay that has settled down on the top of the coarser sediment.1 This it is, that was mixed with the water and made it so thick and turbid; and you can see that the water of the whole river is just as muddy as that with which you filled your pot. Your own experiment has shown you that the water must stand quite still to become clear, and that even then it takes a long time to do so. But the water of the river is all in motion, and being unable to deposit its mud, carries it down with it to the sea. What becomes of it there we shall learn afterwards, but in the meantime it may occur to you to ask where it all comes from, and what must happen if the same thing goes on year after year, as you know it does. The first question is soon answered. 1 This is what is called an experiment, and what I suppose you to have been watching is an observation. It is by these two methods that all our knowledge of nature has been gained. |