Factual data on the evolutionary histories of numerous rivers and water bodies show convincingly that during the last 4500 years the drainage system of the Earth has gone through stages of more or less considerable rearrangement. These rearrangements took place simultaneously with the fluctuations in climate, and thus simultaneously with the fluctuations in the diurnal-rotation regime of the Earth. With the onset of a period of climatic cooling, the rotational velocity of the Earth began to increase, and due to the greater centrifugal forces the drainage system became rearranged in conjunction with the general equatorward shift of all the water. This sort of rearrangement of the drainage system took place during each of the three cold periods. With the onset of a period of climatic warming, the diurnal velocity of the Earth began to decrease, and by virtue of the diminished centrifugal forces the drainage system was rearranged in conjunction with the general shift of water toward the poles. This sort of rearrangement of the drainage system took place during each of the three warm periods (present period included).
In our choice of the rivers and water bodies to be studied, we were guided by certain considerations. First of all, the chronological evolutionary histories of the latter had to be specified somehow or other, by means of data for as long a period as possible. Second, the rivers and water bodies had to be located in the middle latitudes, where the effect of the centrifugal forces is a maximum and where the effect of glaciological loading and unloading is in practice very small. Third, the rivers selected had to flow latitudinally, since in this case their migration shows up the most clearly.
Of all the objects studied by us, the following best satisfied the above conditions: the Black Sea and Caspian Sea, and the Hwang Ho, Amu Dar'ya, Syr Dar'ya, Kura, Kuban', and Don rivers. The effect on the rearrangement of the drainage system of such well-known factors as the quantity and rate of moisture arrival at the surface of the land, the conditions of runoff of this water, the resistance of the land surface, tectonic movements, human intervention, etc. will not be considered at all here. The effects of all these factors will be superimposed onto the periodic rearrangements of the drainage system established by us, but they will not change the general trend of the rearrangements.
Some data on the level fluctuations in individual water bodies and the migrations of certain rivers in their lower reaches are given in Table 2. These variations are compared in the table with the climatic changes (and thus with the fluctuations in the diurnal rotation of the Earth) during the last 4500 years. The water-level variations and river migrations
are compared with a combined graph showing the wetness in the Northern Hemisphere (according to Shnitnikov) and the fluctuations in the level of the Caspian (according to Apollov). The combined graph was taken from Tsekhanskii, 1959, p. 199. The probable climatically induced fluctuations in the Earth's angular velocity are also shown on the graph. Finally, by means of a very schematic curve for the variations in the rotational regime of the Earth, we have endeavored to represent the observational data for the last 300 years (Martynov, 1961).
Unfortunately, the size of the present article does not permit a complete, detailed presentation of the results of our studies concerning the histories of rivers and water bodies(see table). Therefore, we shall limit ourselves to a few general observations about each object, and in certain cases we shall present extracts and diagrams taken from the works of other authors, together with an indication of the main references on the subject. For the sake of brevity, it will not be repeated in each instance that the long period fluctuations in the diurnal-rotation regime, caused by the correspond ing climatic changes, are the direct cause of the river migration and the variations in water level. It will simply be stated that the latter variations are the result of the change in climate (the onset of a warm or cold period). The rivers and water bodies will be considered successively, beginning with those in the east and passing to those in the west.
In the first warm period (Bronze Age) the river turned almost due north at its outflow from the mountains. It then picked up the Peh Ho and Lwan Ho tributaries, flowed to the northern part of the Great China Plain, east of Peking, and discharged into the Liaotung Gulf at 39°30'N. This course of the river was the closest to a north-meridional one, if we take into account the conditions in the locality through which the channel passed at this time. It should be noted that from that time up to the present the course of the river did not ever become as meridional as this again.