344 ON THE MOVEMENTS OF THE EARTHS CRUST. 



work (p. 211) lu'. says : " It is .only by tens of meters thut on the coast 

 of the Cotentin we must reckon the differences between the successive 

 levels of the seas, from the Trias down to the ijresent day." Here we 

 see that the variations of level have taken place with great regularity. 

 Tiie sea has risen, and later on the land has been elevated; and these 

 alternate risings and sinkings have occurred with such regularity that 

 the coastline again and again, at long intervals, has returned about to 

 its old place. 



After this there seems really to be a possibility that our hypothesis 

 is sufficient to explain the displacements of the shore-lines which have 

 taken place. We have hitherto considered the conditions under high 

 latitudes. Under lower latitudes all may sink. Here "Horste" may 

 be formed such as" Suess supposes, and as to the occurrence of these 

 localities Lapparent's criticism is unsatisfactory. He has attacked 

 Suess's theory of "Horste" in its entirety, but he has criticised it spe- 

 cially only for such localities (Colorado, Vosges, Black Forrest, and the 

 central plateau of France) as lie under high latitudes. The localities 

 named have (according to Lapparent) risen more than their environ- 

 ment, which also is quite in accordance with the opinion above devel- 

 oped. But under lower latitudes, when a general sinking takes place 

 in the course of time, resistant parts will form true "Horste" in Suess's 

 sense. And it scarcely goes against our hypothesis to assume, with 

 Suess, that the Indian Ocean is formed by depression, and that Africa, 

 Madagascar, India, &c., are "Horste," parts of the crust which have 

 remained in position, or which have sunk less than the neighboring 

 regions. In these countries, so far as their geology is known at present, 

 there seem to be few marine formations of the Mesozoic and Caiuozoic 

 epochs. 



I have said above that the different parts of the crust may be assumed 

 to have difierent powers of resistance against the interior pressure. 

 This may indeed be concluded from the fact that the surface is uneven, 

 and that old (originally horizontal) formations have been upheaved un- 

 equally at different spots. In other words, there is an inequality of the 

 surface, which has a deeper cause than the operation of eroding forces. 



Changes of the earth's crust in reality happen in the most various 

 degrees at different times. The greatest convulsions occur in the folded 

 mountain-chains, and this has been the case in all geological periods. 

 It is worthy of note that places where great foldings took place in an- 

 cient times seem to have been subsequently unaffected by processes of 

 folding.* For upon the abraded summits of old folds there often lie 

 other old formations in an undisturbed horizontal position. The most 

 highly folded chains are also those in which plications have been con- 



* If the earth's axis, as some astronomers (e. g., Gyltlen) thiuk, may shift its position 

 in the course of time, calculations as to the pressure produced by the lengthening of 

 the day will also change, and the situations of the parts of the crust exposed to the 

 greatest pressure will also shift. 



