the Displacement of Shore-lines. 417 



lias shown that ice, lead, and also oast iron, 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 surroundings. On cutting 

 through such pressed pieces it has been found that the par- 

 ticles or crystals have arranged themselves by a flow-like 

 movement suited to the form of the cavity into which the 

 piece has been pressed. 



We must here also refer to the interesting investigations of 

 Reusch 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 Eeusch, 

 SUurfossiler og pressede Konglomerater i Bergensskiferne, Univ. 

 Progr. Christ/an/a, 1882, pp. 15, 117.) 



By reason of the enormous pressure which prevails in the 

 interior of the earth, it must be supposed 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 parts 

 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 liigher latitudes. There is, as 

 Darwin indicates ('Nature,' Sept. 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 may 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 Fysiken, Stockholm, 1861, pp. 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 pressures we 

 find no permanent change of form, tliis is because the force 

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

 when it has a greater resistance to overcome, depends upon 

 time. " By tension," says Schi0tz [Lmrebog i Fysik, Christi- 

 auia, 1881, p. 65), " lengthening constantly increases, although 

 very slowly, after it first commences ; therefore a weight which 

 has acted for a short time will not produce persistent elonga- 



Pldl. Mag. S. 5. Vol. 27. No. 168. May 1889. 2 E 



