544 THE POPULAR SCIENCE MONTHLY. 



dogmas wliicli forbid any interpretation of the phenomena other 

 than that of fixed rules which are more worthy of the sixteenth 

 than of the nineteenth century. Instead of weighing the evi- 

 dence and following up the consequences that should ensue from 

 the assumption, too many attempts have been made not unnatu- 

 rally by those who hold this faith to adjust the evidence to the 

 assumption. The result has been strained interpretations framed 

 to meet one point, but without sufficient regard for the others. 

 We repeat that we would not for a moment contend that the 

 forces of erosion, the modes of sedimentation, and the methods of 

 motion, are not the same in Mnd as they have ever been, but we 

 can never admit that they have always been the same in degree. 

 The physical laws are permanent ; but the effects are conditional 

 and changing, in accordance with the conditions under which the 

 law is exhibited. 



Such are the barriers which seem to us seriously to retard the 

 advance in one direction of an important branch of theoretical 

 geology, while in another it is fronted by the stern rules of an ap- 

 parently definite calculation. 



We must ask to be forgiven if we can not accept the conclu- 

 sions of physicists respecting the extreme rigidity of the earth 

 and the immobility of the crust as conclusive. That the rigidity 

 is now very great as great, we will admit for argument's sake, 

 as if the globe were of glass or steel may be as asserted, but that 

 conclusion can only be accepted in so far as it conforms to the 

 facts of geology. Were the data on which the conclusion is based 

 fixed and positive, like those on which the laws of gravitation and 

 light are established, there would be nothing for the geologist to 

 do but to bow to the decision of the physicist, and, if possible, re- 

 vise his work. But in this case the tidal observations, on which 

 the calculations of rigidity are mainly based, are of such extreme 

 delicacy that, failing as the hypothesis does to satisfy the require- 

 ments of geology, the geologist may be excused for his dissent, 

 pending further inquiry. Should this tend to confirm the extreme 

 rigidity of the globe, we must seek for some explanation of earth 

 movements consistent with that rigidity. It is indisputable that 

 up to the latest geological period that touching on our own 

 times the mobility of the crust was very considerable, for the 

 raised beaches of Europe and of the Mediterranean prove conclu- 

 sively that in that period extensive tracts were raised at intervals 

 to heights of from ten to six hundred feet or more above their 

 former levels. It is difficult to conceive that a globe, of which 

 the crust was then so mobile, could have acquired, in the com- 

 paratively short interval between the latest of the beaches and 

 our own time, so great a rigidity as to be practically immobile. 



For similar reasons the conjoint conclusion that the crust of 



