54 THE TIDAL PROBLEM. 



The assigned equatorial shrinkage from reduction of rotation since the 

 3.82-hour rotation-period is 180 miles, which is to be compared with the 

 minimum 64 miles or the maximum 128 miles of the above estimate. Of 

 course, it must be recognized that the 180 miles covers a period preceding 

 the known Archean, which is not embraced in the latter figures; but if an 

 allowance of two-thirds be made for this, the remaining 60 miles vertical 

 shrinkage still bears a sufficiently large ratio to the stratigraphical estimates 

 to make its effects certainly discernible, when the contrasted influences 

 in polar and equatorial regions are brought into comparison. 



The computation for maximum rotational change gives a meridional 

 elongation of 495 miles; the stratigraphic estimate gives a meridional 

 contraction of 400 and 800 miles minimum and maximum respectively. 

 Allowing two-thirds of the 495 miles for the period preceding the known 

 Archean, there remain 165 miles of elongation to reduce the effects of the 

 400 or 800 miles of contraction. 



Combining equatorial and polar effects, the case stands 777 (400+377) 

 vs. 235 (400-165), on the minimum basis, and 1,177 (800 + 377) vs. 635 

 (800 - 165), on the maximum basis, when two-thirds of the retardation is 

 assigned to pre- Archean times. It would seem that differences of this order 

 of magnitude should be clearly manifest in the phenomena. 



THE EVIDENCE FROM THE HYDROSPHERE. 



If there be any doubt about the practicability of detecting the influ- 

 ence of any great change in the rotation of the earth by the distinctive 

 features of the deformation of its shell, we certainly have a very delicate 

 means of detecting deformations in the position of the sea-level relative 

 to the land. The position of the sea-level has been recorded by a series of 

 shallow-water and shore deposits extending from the Cambrian period to 

 the present, and this record was made with sufficient frequency and fidelity 

 to answer every purpose of an inquiry of this kind. To a much greater 

 extent than has usually been recognized, the known stratigraphic series 

 is the product of shallow water, as shown by shallow-water life and appro- 

 priate physical evidences. In many cases some latitude must be allowed 

 in the interpretation of these criteria of depth, but this can be the source 

 of no essential error in a problem of deformation whose units are miles 

 rather than feet; but, if required, a sufficient number of cases of irreproach- 

 able accuracy can be given, for at not a few geologic epochs there were 

 emergences and submergences between which some stage of the transition 

 marks the relations of the water surface to the land with positiveness and 

 exactness. If, for instance, we know that in the critical regions, whether 

 poleward or equatorward, a given horizon has been above the water- 

 level and below the water-level respectively at two successive stages, we 

 know that between these stages it was absolutely at the water-level. ^ By 

 means therefore of the successive emergences and submergences of given 

 horizons, the relations of the sea to the land can be determined very accu- 

 rately for a sufficient number of geological stages to be wholly decisive in 

 such a problem as that in hand, and approximately for most of the other 

 periods. 



