1883.] 467 [Crosby. 



of the primitive or unstratified crust is any where exposed. Fur- 

 thermore, the old crystalline or Eozoic formations which, accord- 

 ing to Professor Dana, formed the first land and the nuclei about 

 which the present continents have been developed, are of enor- 

 mous thickness. The Eozoic rocks of the Rocky Mountains, 

 Canada, New England, and the southern Appalachians have an 

 average thickness of probably not less than 50,000 feet, and many 

 geologists would say 100,000 feet. Where was the land whose 

 waste afforded the material for building these tens of thousands 

 of feet of strata ? It must have existed somewhere. It was 

 probably outside the borders of the modern continents ; and it 

 was certainly land whose site was subsequently occupied by the 

 sea. 



Thus it is clear that extensive bodies of land, in other words 

 continents, were in existence before any part of the land of to- 

 day had appeared above the sea. 



But, without pressing farther the question as to how, if the 

 theory in question is correct, the modern continents ever came 

 to have a beginning, let us advance a step and look for the source 

 of the materials composing the subsequent additions to the con- 

 tinents, including the Paleozoic and all later formations. Accord- 

 ing to Professor Dana, they were derived entirely from the com- 

 paratively small Eozoic areas. This, however, means not less than 

 ten, and possibly twenty, miles of erosion, and necessarily im- 

 plies either that this primitive land had originally an incredible 

 height, or that during the course of geological time it has been 

 constantly renewed by elevation as fast as worn away. But what 

 are we to think of the original volume of formations which could 

 suffer this enormous waste and still have a thickness measured 

 by miles? We could not emphasize more strongly the absolute 

 necessity of extensive pre-Eozoic continents to serve as a source 

 of Eozoic sediments. 



If the continents, since their first appearance, have been ele- 

 vated ten to twenty miles and are still rising, they must rest on 

 a plastic stratum. Thus Professor Dana's theory, when rigor- 

 ously followed out, leads to the conclusion that the continents 

 are essentially great upward bendings of the crust. A large part 

 of this stupendous elevation must have occurred, if at all, since 

 the early Paleozoic beds were deposited ; and consequently they 



