IN THE DEGRADATION OF THE LITHOSPHERE. 389 



duced any considerable continental mass ; nor should the value of 

 a factor be judged simply from the lateral extent of its spread. 

 The investigations of Barrell already referred to would certainly 

 indicate if not prove that marine aggression has played a most im- 

 portant part in the leveling of the land surface. 



It may be worth while to note further that jointing is not simply 

 a vertical matter, it seems so under certain forms of atmospheric 

 attack but under the transporting power of a sea aggression climb- 

 ing the land surface the development and the existence of horizontal 

 joint lines will accelerate the rate of land degradation in a manner 

 analogous to the acceleration of stream erosion due to change of 

 level. 



It is interesting that almost all of the illustrations chosen by 

 Geikie show the controlling action of joints to shape not alone the 

 clift's but to accelerate the action of marine erosion yet he gives 

 but incidental reference to the presence of joints, and seems to lay 

 most emphasis upon the aerial agents though each illustration given 

 shows in nearly every instance the effect of the controlling action of 

 joints. Again I venture to state that the object of this study in 

 most part is not to claim for either land or marine degradation the 

 superiority as a universal agent of land surface reduction but to 

 try to establish the fact of the presence of one factor which may 

 be regarded as controlling both and which under conditions, favor- 

 able now to land erosion, now to sea erosion, enters as the dominant 

 medium for shaping the resulting surface of the stony portion of 

 the earth more technically known as the lithosphere. And that in 

 the nature of the relation of the three elements of the earth, atmos- 

 phere, hydrosphere, lithosphere, the attempt to restrict the forces of 

 lithosphere degradation to an assumed base level fixed by the sea 

 level is an untenable position. Untenable because of the fractured 

 nature of the rock mass itself and also because of the fact that the 

 sea level is not constant, so that whether the sea level move up or 

 down either from the shifting of the land mass or from the sea 

 itself there will still be presented below sea level the constant factor 

 of joint weakness in the mass of the earth itself to induce disin- 

 tegration and further leveling ; connecting in this manner land or 



