232 GEOLOGY. 



continents to be submerged by this process would, therefore, stand at 

 that height above the present sea-level. The disturbed condition of 

 the Proterozoic formations, and the truncated condition of their up- 

 turned beds, may be taken as good evidence that the continents stood 

 forth from the sea rather prominently at the close of the Proterozoic 

 era. The actual mass of the continents is not known, and it is not very 

 essential for present purposes. The higher the continents, the more 

 the material available for removal to the sea and so for the lifting of the 

 surface when deposited beneath it, and the more the lifting needful 

 to submerge the continents ; while the lower the continents, the less the 

 material available for lifting the sea, and the less lifting needful to cause 

 it to cover the land. It is a case of reciprocal relations and of mutual 

 accommodation, in any event. The result is certain in any case, if 

 the time be long enough and deformation does not interfere. Defor- 

 mation is a possible bar, as well as a possible aid, to the wide spreading 

 of the sea on the land. A satisfactory explanation of the covering of 

 great tracts of land by the sea may therefore require the exclusion, or 

 the limitation, of profound crustal movements, rather than their 

 participation. 



The direct evidence of gradation in the Cambrian period is clear 

 and firm, for there is no ground to doubt that the main body of the 

 Cambrian sediments was eroded from the land and deposited in the 

 sea. This gradation tended to lower the land and raise the sea. We 

 are safe, therefore, in concluding that surface action was a participant 

 in the result attained. There is much evidence that considerable 

 progress was made toward the base-leveling of the American conti- 

 nent, and of other continents as well, before the close of the Cambrian 

 period. The very fact of the spreading of the sea so widely over the 

 interior of a continent, and of the laying down of a relatively uniform 

 and not very thick formation of sandstone over such broad areas, on 

 a surface which approached a plane, though underlain by beds which 

 are commonly much deformed, is in itself evidence of extensive level- 

 ing by degradation. 



Now base-leveling implies a nearly undisturbed attitude of the land 

 and sea during its progress, and hence in itself favors the view that no 

 great deformation affected the continent while it was going on. In 

 harmon}' with this view, there is an absence of direct evidence of a 

 profound deformation during the Cambrian period. There is there- 



