ON THE MOVEMENTS OF THE EAUTh's CRUST. 335 



that ice, lead, and also castirou, even at ordinary temperatures, may 

 be squeezed so strongly that their interior parts change their relative 

 positions like particles in a fluid. Iron, in the solid state, by strong 

 pressure, is squeezed into cavities and adapts its form to the surround- 

 ings. On cutting through such pressed pieces it has been found that 

 the particles or crystals have arranged themselves by a flow-like move- 

 ment suited to the form of the cavity into which the piece has been 

 pressed. 



We must here also refer to the interesting investigations of Keusch 

 upon pressed conglomerates. Under the strong pressure which has 

 acted in the earth's crust, the pebbles in conglomerates are squeezed 

 out into lance-shaped bodies, and these bodies have even become folded. 

 (See Reuscli, SUurfossiler og "pressede Konglomerater i Bergensskifcrnc, 

 Univ. Progr. Ghristiania, 1882, pp. 15, 117.) 



By reason of the enormous pressure which prevails in the interior of 

 the earth, it must be supj)osed that masses from a certain depth are 

 more or less in a plastic state. A constant lengthening of the sidereal 

 day will cause the equatorial i)arts to increase in weight. So long as 

 the earth does not change its form, a constantly increasing weight will 

 act upon the internal mass from lower towards higher latitudes. There 

 is, as Darwin indicates {Nature, September 2, 1886, p. 422), reason to 

 believe, that finally, when the tension has reached a certain amount, 

 the earth will yield. A flow of plastic mass will be directed towards 

 higher latitudes, and persist until the earth has approximated to the 

 form suitable to the length of the sidereal day. When we consider the 

 numerous testimonies as to changes in the solid crust of the earth, and 

 the frequent elevations and depressions of the solid land relatively to 

 the sea, we uuiy well agree with Darwin, that this view may claim more 

 probability than that of Thomson and Tait. 



Wertheim has proved by experiment (according to Fock, Ldrohok i Fysi 

 keiij Stockholm, 18(51, i)p. 202, 219) that there is really no definite limit 

 of elasticity for any matter, but that they all, by the action even of 

 quite feeble forces, undergo small persistent changes, especially if these 

 forces have acted for a somewhat long time. When with feeble press- 

 ures we find no permanent change of form, this is because the force 

 has not acted long enough. The action of the force, therefore, when it 

 has a greater resistance to overcome, depends uj)on time. By " tension," 

 says Schif/»tz {Ltvrebog i Fysik, Christiania, 1881, p. 05), "lengthening 

 constantly increases, although very slowly, after it first commences; 

 therefore a weight which has acted for a short time will not produce 

 persistent elongation such as it would be if it were allowed to act for 

 a longer time. This applies not only to tension, but generally; and 

 hence it comes about that wires slacken in course of time, and that 

 beams bend little by little. A thread is worn out by less force when 

 the pressure is long continued than when it is applied for a shorter time." 



It seems to me that here we have a force which may be capable of 



