46 THE TIDAL PROBLEM. 



if the deductions which have heretofore been drawn from the older cos- 

 mogonic and geophysical conceptions are true, there should be geological 

 testimony to support them. We turn therefore to the geological evidences 

 with heightened interest. 



THE GEOLOGICAL EVIDENCES. 



Perhaps the most important of the geological lines of approach to the 

 rotational problem, is found in the evidences of an appropriate change 

 or lack of change of the earth's form. At least it is this problematic change 

 of form that gives the subject its obvious importance in diastrophism, to 

 which this discussion is a preface. If the rotation of the earth were once 

 appreciably faster than now, either the form of the lithosphere would have 

 been more oblate than it is at present, or the surface-waters would have 

 been accumulated at the equator by the increased centrifugal force, or 

 both actions would have taken place conjointly; and a change from this 

 configuration to the present one must have followed. If the lithosphere 

 has changed its form appreciably within known geological times owing to 

 reduction of rotation, such a change should be manifest in its structural 

 deformations, especially in the deformations of the early ages. If the 

 lithosphere has not essentially changed its form because of reduced rota- 

 tion, but the waters served as the accommodating factor, this, if it were 

 of sensible amount, should have been manifested by deposits of the kinds 

 that imply prevalent and deep submergence in the equatorial regions 

 and by erosions signifying prevalent and pronounced emergence in high 

 latitudes in the former ages of higher rotation, and by the reverse in the 

 later ages, both of which would be shown by the geological records of those 

 regions. 



THE EVIDENCES FROM THE LITHOSPHERE. 



The bearing of a possible change of form, assignable to a change of 

 rotation, on terrestrial diastrophism has long been recognized in some 

 measure by geologists, but the first attempt to reduce it to numerical terms 

 seems to have been that made by President Van Hise several years ago.' 

 He inspired Prof. C. S. Slichter to make the computations necessary to 

 show in numerical terms what would be the reduction in surface area if 

 the rotation were changed to the degree postulated in Darwin's interpre- 

 tation of the past history of the earth and moon. It was thought by 

 him sufiicient to base the computations on the convenient hypothesis of a 

 homogeneous density. The change of surface area was shown to be large 

 and this made it clear that, if such a change of rotation has taken place, it 

 is an important factor in deformation. Even if the chief deformation took 

 place early in the history of the earth, the effects should be apparent still 

 in the inheritances of the regions most affected, and the record should show 

 them. For the purpose of a more critical study of the subject, Professor 

 Slichter has been kind enough to recompute for me the requisite data on 

 the basis of a distribution of internal density as near that of the actual 

 earth as our present knowledge permits. For this purpose Laplace's law 



^ Van Hise, Jour. Geol., vol. 6, pp. 10-64, 1898; Slichter, ibid., vol. 6, pp. 65-68, 1898. 



