356 GEOLOGY 



blocks which were moved in different degrees, and were often tilted 

 individually (Fig. 287) . At the surface, these blocks are separated 

 by fault-planes, but below, some of the faults pass into flexures. 

 Most such flexures are monoclinal. Plateau-forming movements 

 are to be compared with the continent-forming movements, rather 

 than with mountain-foldings, differing from the former chiefly 

 in magnitude. Plateaus may be regarded as parts of a continental 

 mass that have suffered special additional movement. Plateaus 

 stand in some such relation to continents, as one fault block of a 

 plateau does to the whole plateau. They are probably to be re- 

 garded as the results of body deformations, while the mountains are 

 the result of the folding of the shell, affecting only a few miles of the 

 outside. 



3. Continent-forming movements. These are widespread move- 

 ments affecting large masses of the body of the earth, if not its 

 whole outer portion. Two or more continents are often affected 

 by similar movements at the same time, and it is the view of many 

 geologists that all continents are usually affected simultaneously 

 by movements of a like kind, resulting in emergence or submergence, 

 while the ocean basins are affected by movements of the opposite 

 phase. These are thus thought to be body movements. The 

 depression of the basins and the relative elevation of the continents 

 are regarded as reciprocal parts of a world-wide adjustment. While 

 well supported both by observation and theory, this view cannot 

 be said to be universally accepted. Movements of this class seem 

 to have started early in the history of the globe, and to have 

 been renewed from time to time, rejuvenating the continents and 

 developing the basins. Under the view that the earth is essen- 

 tially solid throughout, these movements are regarded as deep- 

 seated deformations, while the mountain folding is regarded as 

 but the wrinkling of the earth's skin to fit its changed body. 



Downward movements are regarded as the primary ones, and 

 horizontal movements as a necessary result of them. The primary 

 cause is believed to be an increase of the density of the earth, 

 actuated by gravity and the molecular and sub-molecular attrac- 

 tions. The master movement is thought to be the sinking of the 

 great basins, whose specific gravity is greater than that of the con- 



