56 Probable Astronomical Causes of 



nearly what it ought to be, by the theory of gravitating and 

 centrifugal forces. If, then, the spheroidity is just what it 

 should be from the earth's present rate of axial revolution, 

 any greater rate of revolution in the past must necessarily 

 have resulted in a less spherical form than that now ob- 

 taining. 



I. Let us see what would be the result of any change in form 

 such as the one suggested ; that is, from a spheroid, the 

 difference of whose diameters was excessive, to one in which 

 the two diameters approximated to each other. 



First. The equatorial diameter and circumference would 

 be shortened, and as the dimensions of the crust or solid 

 covering of the molten nucleus within would remain constant, 

 a puckering in such crust would be the natural sequence. 

 The force, also, causing these puckers, would be in the 

 direction of the parallels of latitude, so that the coiTUgations 

 (if I may so term them) would run in a strictly meridianal 

 direction. This phenomenon of the puokers would be 

 common over all tropical and semi-tropical regions, save in 

 the exceptional cases to be presently mentioned. 



Secondly. The polar diameter would be increased. Hence, 

 at the arctic and antarctic circles, the molten matter within 

 would tend to swell outwards, and as the same would act 

 upon a rigid crust, such crust would be fractured in a stellar 

 form, the rays proceeding from each pole as a centre. 



Thirdly. Between these two regions of contrary disturb- 

 ances would be one of quiescence. This region would 

 correspond, or nearly so, with the temperate zone. 



II. It is interesting to see whether marks of these supposed 

 disturbances are anjnvhere apparent in the arrangement of 

 strata, and other physical features of the earth's surface. 



First. In Victoria, as was previously stated, the strike 

 of the strata is, generally, nearly north and south. This 

 strike seems to prevail over very large portions of the 

 Continent. 



Secondly. In a paper by Mr. Searles Wood, appearing in 

 the Philosophical Magazine, this peculiarity of strike is stated 

 to be incidental to palseozoic strata nearly all over the 

 world ; that is where such strata are at all contorted. 



Thirdly. The principal mountain systems in which 

 palaeozoic rocks prevail run ' nearly north and south, as 

 witness the Andes, the Rocky Mountains, the Ural, and the 

 Australian Alps. Near the equator in Brazil, too, are 

 numerous chains of mountains, all of which, by Johnson's 



