370 EHREXFELD— JOINTING AS A FUNDAMENTAL FACTOR 



its various aspects, and also under the attack of the forces of the 

 sea, these joints have become great Hues of weakness, so that the 

 whole outer portion of the lithosphere is here undergoing a profound 

 and far-reaching disintegration. This sequence of events of re- 

 peated loading by sediment and erosion of the surface by ice caps 

 has produced a wornout condition of the lithosphere structure at 

 this point, so that even if we regard the Canadian Shield, and 

 analogously the Baltic Shield, as one of the fixed segments of the 

 earth, we may still observe that it is undergoing degradation just as 

 other surfaces of the earth are undergoing degradation. The fact 

 that it may be regarded as fixed so far as up and down motion is 

 concerned does not conceal the further fact that under the loading 

 indicated the mass has lost its elasticity as a steel mass will even- 

 tually lose its elasticity and will be subjected to falling apart. It is 

 possible, then, to regard even the fixed positive elements or horsts 

 as subject to disintegration and reduction through combined jointing 

 and marine aggression, in other words, it is possible, in my estima- 

 tion, to demonstrate a reduction of the lithosphere below sea level. 

 As 1 conceive the situation we are witnessing, in short, the destruc- 

 tion of a continental mass through the combined efifect of forces 

 from without and from the inherent weaknesses which have been 

 brought about through past geological conditions ; that finally we 

 have here not so much a rise or fall of land as we have of litho- 

 sphere planation or reduction upon a grand scale, and that this 

 planation is hastened and largely induced through the weaknesses 

 in the continental mass itself. 



It may further be seriously questioned whether the " peneplain " 

 of this Canadian area may not eventually have to be regarded as due 

 rather to marine denudation rather than to atmospheric erosion. 

 One of the objects of this study has been to consider the old and 

 now somewhat neglected subject of marine denudation in connec- 

 tion with the modern study of joints. Further details of this will 

 be considered later in this discussion. 



Since there is stratigraphic evidence for believing in the exist- 

 ence of former land connection across the northern hemisphere with 

 perhaps former water channels leading down into the present Europe 

 and North America the question of the disintegration and degrada- 



