900 



SCIENCE. 



[N. S. y&h. IX. No. 235-., 



nate stage in the earth's existence the 

 numerical results of a computation based 

 on a full-grown moon may need radical re- 

 vision. 



Furthermore, the agencies which are as- 

 sumed to have accelerated the rotation of 

 the earth in its earlier history must not be 

 neglected. If they may safely be assumed 

 to have been competent to give the earth a 

 rotary speed sufficient to detach from itself 

 the matter of the moon, as is postulated in 

 the Laplacean and the fission hypotheses in 

 common, the same agencies, if more evenly 

 distributed in time, might prolong the pe- 

 riod of acceleration so' that it should be 

 coincident with that of tidal retardation 

 and offset it in any degree that falls within 

 the legitimate limits of assumption. We 

 encounter here again, in another form, a 

 deduction from the assumption of a very 

 rapid concentration of the matter ingath- 

 ered to form the earth and moon, and the 

 consequent exhaustion of its energy in an 

 early stage. If, however, the concentra- 

 tion were less rapid and less complete in 

 the early history of the earth, as is postu- 

 lated by the accretion theory, as herein 

 entertained, acceleration might be far less 

 advanced in the earliest stages and be 

 greater in the later stages. Hence the re- 

 tarding effects of tidal friction may have 

 been more effectually antagonized by the 

 shrinkage of the earth during tlie progress 

 of geological historj'. Mr. Moulton has 

 computed the effects of the internal change 

 of metal and rock material, assumed in a 

 hypothetical case on a previous page, on 

 the speed of rotation of the earth, and found 

 that it would accelerate the then-current 

 rate, whatever it was, about one fifth. If, 

 therefore, the delayed central concentra- 

 tion left some notable part of the accelera- 

 tion to be gained during the period of 

 geological history, and if, at the same time, 

 a slow aggregation of the moon delayed its 

 effectual tidal influence upon the earth and 



the reciprocal influence of the earth upon 

 it, the whole history may be nO'tably affected 

 in the direction at once of less maximum 

 speed and of less retardation, *. e., of more 

 near approach to uniformity. 



If we turn to the geological data that 

 bear on the question of former high rotation 

 and subsequent retardation we find ample 

 support for profound skepticism regarding 

 the applicability of the tidal argument. As 

 pointed out by Lord Kelvin, if the rotation 

 of the earth were once notably greater than 

 at present it should have resulted in an 

 oblateness of the spheriod such that the 

 equatorial regions would now be all dry 

 land, unless the body of the earth were de- 

 formed to correspond to the slackening 

 rotation in an almost perfect manner. But 

 there is not the slightest evidence in the 

 configuration of the earth of such an equa- 

 torial land tract. The equatorial belt is 

 notably oceanic rather than otherwise. 

 Reciprocally, there should have been, with 

 the gradual slackening of the earth's rota- 

 tion, an accumulation of the oceanic waters 

 about the poles, but there is no geological 

 evidence of such an accumulation in any 

 appreciable degree. In the Arctic regions, 

 as exemplified in Greenland, Spitzbergen 

 and the Arctic islands of America, there 

 are ancient shallow water deposits which 

 lie both above and below the present oceanic 

 level. These deposits range throughout 

 the Paleozoic and represent in some less 

 degree both the Mesozoic and Cenozoic 

 eras. The nature of these shallow-water 

 deposits is such that they cannot have been 

 formed at great depths below the oceanic 

 surface, so that, with the allowance of a 

 few hundred feet, it is possible to locate 

 the ancient horizons relative to the crust of 

 the earth, at most or all of these periods. 

 From these it may be inferred with great 

 confidence that the ancient ocean surface 

 n the Arctic regions was in numerous 

 stages of Paleozoic, Mesozoic and Cenozoic 



