MOVEMENTS AND DEFORMATIONS OF THE EARTH'S BODY. 545 



sisted chiefly in the further sinking of the basins and the further pro- 

 trusion of the land, save as the latter has been cut do^\Ti by erosion. 

 Incidentally, the ocean-basins have probably been extended and the 

 continents restricted. On the other hand, the continents have been 

 built out on their borders by wash from the land, and the waters of the 

 ocean have been somewhat lifted by the deposition of sediment in their 

 basins. It is estimated that the cutting away of the present continents, 

 and the deposition of the material in the ocean-basins, would raise the 

 sea-level about 650 feet. (R. D. George.) 



Relations of these movements in time. — The folding movements seem 

 to have had extraordinar}^ prevalence in the earliest ages, for the Archean 

 rocks are almost universally crumpled, and often in the most intricate 

 fashion. There is no sign that the folding was then limited to the 

 borders of the continents; it seems rather to have affected the whole 

 continental surface. After the beginning of the well-known sedimentary 

 series, crumpling appears to have taken place chiefly at long intervals, 

 thus marking off great time-divisions, and to have been confined at 

 any given stage to certain tracts, chiefly on the borders of great seg- 

 ments of the earth's crust. 



Concerning the plateau-forming movements in the past, knowledge 

 is very meager, as the detection of plateaus of ancient times is more 

 difficult than the detection of folds. Gentle warpings have apparently 

 been in progress at all times. 



Relations of vertical to horizontal movements. — The downward move- 

 ments are unquestionably the primary ones, and the horizontal ones are 

 secondary and incidental. The fundamental feature is doubtless 

 central condensation actuated by gravity, and the master movements 

 are the sinkings of the ocean-basins. The great periodic movements 

 that made mountains and plateaus, and changed the capacity of the 

 ocean-basins, probably started with the sinking of part or all of the 

 ocean-bottoms. In the greater periodic movements, probably all the 

 basins participated more or less, but some seem to have been more 

 active than others. For example, in the last great mountain-making 

 period, the Pacific basin seems to have been more active than the Atlan- 

 tic, while in the similar great event at the close of the Paleozoic, the 

 opposite seems to have been true. The squeezing up of the continents 

 doubtless took place simultaneously with the settling of the basins. 

 The true conception is perhaps that the ocean-basins and continental 



