REPORT OF THE DIRECTOR 10,20-21 143 



We saw in the preceding chapter that Chamberlin, in the " Origin 

 of the Earth " adduces the influence of oscillating rotation and 

 tidal strains for the growing period of the earth, only leaving to 

 later shrinkage the leadership in shaping the earth after growth 

 had ceased. The same author had already in an earlier paper (in 

 " The Tidal and other Problems," 1909 by Chamberlin et at.) 

 investigated the possible retardation of the earth's rotation through 

 the friction of the water tides and the tides of the lithosphere. It 

 is shown, in this suggestive publication from computations by C. 

 S. Slichter, that when the earth had a rotation period of 3.82 hours 

 its equatorial circumference was 1131 miles greater than it is at 

 present, while the meridional circumference was 495 miles less. 

 " In changing to the present form, the tract immediately under 

 the equator must have become shorter by 1131 miles. The 

 tracts under the parallels adjacent to the equator north and south 

 would have become shorter by less amounts, those still farther 

 away by still less amounts, until a little beyond 30 latitude, north 

 and south, parallels are reached under which the crust would have 

 theoretically remained unchanged so far as this immediate factor 

 is concerned." There is hence a neutral zone at about 35 latitude, 

 north and south, and beyond this are large areas of expansion. 

 We would then have a zone of powerful compression at the equator 

 and two polar caps of similar extensive tension. Chamberlin 

 estimates that the equatorial tract under such conditions must 

 fold, crumple and overthrust on itself after the familiar fashion 

 of folded mountains to such an extent that, using Heim's estimate 

 of 74 miles of the crustal shortening for the Alps, it would require 

 15 ranges of the magnitude of the Alps across the equator, or 28 

 ranges of the order of the Pennsylvanian Appalachians (using 

 Lesley's estimate). 



Professor Chamberlin concludes (op. cit., p. 49) that no such 

 condition is suggested "by an equatorial belt of land, much less 

 an elevated girdle accidented by cross folds, or knots, or contorted 

 protuberances," nor is there any evidence of the truncated remains 

 of these. While this is true of the present condition of the equatorial 

 belt, it seems, however, that it may well have been different in regard 

 to the Precambrian equatorial belt, for there we not only have 

 evidence of an equatorial belt, the Archi-Gondwana, which, if it was 

 not continuous around the earth, quite probably reached three- 

 fourths around; and what seems still more significant, that belt 

 was provided with a complete system of strong north-south folds 

 such as would be postulated by an equatorial compression due to 



