544 GEOLOGY. 



the surface, they are separated by fault-planes, but below, some of them, 

 and perhaps most of them, pass into flexures. Most of these flexures 

 are of the monoclinal type (p. 516), which dynamically means much the 

 same as a fault; but some of them maybe of the compressive type, with- 

 out inconsistency with vertical fault-relief above. Research has not yet 

 covered thoroughly any great plateau, and knowledge of this class of 

 movements is less complete than that of folding by lateral thrust, and 

 it has a less ample place in the literature of the subject. The plateau- 

 forming movements are, however, much more massive than the moun- 

 tain-folding movements, and stand next in magnitude to the continent- 

 forming movements. Plateaus may be regarded as smaller platforms 

 superposed on the continental platforms. 



In the ocean-basins, there appear to be raised platforms of the plateau 

 type, and there are remarkable ''deeps" that have the aspect of anti- 

 plateaus. 



Continent-forming movements. — True continent-forming movements 

 appear to have antedated the earliest known sediments. As far back 

 as we can read the sedimentary record, the continents seem to have 

 been well established, and there is little evidence that they have since 

 been fundamentally changed. It is true that some very eminent geolo- 

 gists have rather freely connected formations on one continent with 

 formations having similar faunas on an opposite continent, by a hypo- 

 thetical conversion of the intervening ocean-bottoms into land or shallow 

 water; but most such faunal relations can be explained almost equally 

 well by migration around the coasts, or at most by mere ridge-connec- 

 tions. The paucity, if not total absence, of abysmal deposits in the 

 strata of the continents, taken with the persistence of terrestrial and 

 coastal faunas, leaves little room for assigning an interchange of position 

 between abysmal depths and continental elevations, and vice versa. 

 Dynamic considerations also offer grave difficulties. The doctrine of 

 the persistence of continents probably ought not to be pushed so far as 

 to exclude shallow water, or even land, connections between South 

 America, Antarctica, Australia, India, and South Africa, directly or 

 indirectly, at certain stages of geological history. Without forming 

 final conclusions as to the measure of the change which the continents 

 have suffered during known geological history, it is safe to conclude 

 that the continents and ocean-basins were in the main formed very 

 early in the earth's history, and that subsequent changes have con- 



