OF THE EAETBl's AXIS OF FIGURE. 43 



ground for believing that the effect has, in point of fact, been pro- 

 duced. 



21. Now, if we have regard to the existing distribution of land 

 and water, the first point that calls for attention is', that the joint 

 effect of all the denudations at present in progress is not cumula- 

 tive but residual. It is an effect resembling the resultant of a num- 

 ber of forces rather than their sum. In the case of some rivers 

 their effects tend to concur ; in the case of others they tend to neu- 

 tralize each other ; there are other cases in which the effects would 

 be but small in proportion to the amount of denudation ; and it may 

 be added that concurrence or the reverse may take place in the effects 

 produced by rivers very far apart. In illustration of these points 

 I will apply the rules enunciated in the note to art. 10 to some of the 

 great rivers, observing that I assume that the matter they transport is 

 carried from the upper regions of the rivers to their deltas, a supposi- 

 tion sufficiently true for present purposes. The great rivers of Siberia 

 tend to shift the north pole on a meridian of about 100° E. long, 

 (rule d) ; the Mississippi tends to shift the north pole on a meridian in 

 about 90° W. (rule c), i. e. on the prolongation of a meridian in about 

 90° E. The effects of the Mississippi therefore tend to neutralize those 

 of the Siberian rivers. A case of concurrence is that of the Dnieper, 

 Don, and Volga, on the one hand (rule 6), with the Nile (rule a), on the 

 other, their joint tendency being to displace the north pole on the pro- 

 longation of a meridian in about 40° E. long. In these cases the rivers 

 flow on the whole from N. to S. or from S. to N. Another case of 

 concurrence is that of the great rivers of China, which, on the whole, 

 flow from west to east and have a mean longitude of about 110 E., so 

 that their tendency is (rule e) to displace the north pole on the meri- 

 dian of about 20° E. ; consequently we have here also a case of neutra- 

 lization; for the group formed by the great rivers of China, has a nearly 

 opposite tendency to that of the group formed by the Dnieper, Don, and 

 Volga on the one hand and the Nile on the other. As an instance of 

 a denudation which tends to have but a small effect in comparison 

 with its amount, we may take that produced by the Amazons, the 

 course of which, running nearly along the equator, has little ten- 

 dency to affect the position of the pole. Another case is that of the 

 Indus, Ganges, and Bramaputra ; they cannot be reckoned to trans- 

 fer matter through more than about 10° of latitude ; their tendency, 

 however, is to increase the displacement produced by the Siberian 

 rivers (rule c). 



22. These cases are cited merely to illustrate the point that the 

 joint effect of all the denudations going on at a given time is not 

 a simple accumulation of small results, but is a residual or resultant 

 effect of many separate tendencies which in a greater or less degree 

 neutralize each other. To ascertain quantitatively what the total 

 effect of all these tendencies is, the effects of matter transported by 

 icebergs as well as by rivers would have to be taken into account, 

 and the effects of small as well as of large rivers. Eor the solution 

 of such a question the data do not, I believe, exist. But it is not 

 unlikely that at present there is a predominating tendency to shift 



