HABITAT OF THE EARLY VERTEBRATES 405 



Moreover, if the land were unprotected by vegetation, the 

 rate of transportation of loosened surface materials would prob- 

 ably have been too great to permit complete chemical dis- 

 integration. As fast as crystalline grains were separated from 

 their fellow grains by disintegration acting at their contacts, 

 or along cleavage planes, they would doubtless have been 

 promptly carried away to sea and the sands and silts would have 

 been arkose in type. But as far down as the Cambrian at least 

 they are distinctly not so, as a general rule. They are as pro- 

 nouncedly disintegration-products as in any later age. The 

 Upper Cambrian sandstone of the American interior is a most 

 typical example of a thoroughly disintegrated product. The 

 Huronian series, as developed about the Upper Great Lakes, 

 bears scarcely less distinctive evidence of the dominance of dis- 

 integrating agencies than the Mesozoic and Cenozoic terranes 

 on whose origins the influence of an ample clothing of vegeta- 

 tion wrought its full effects. 



Still further, the voluminous carbonaceous deposits of the 

 Huronian give support to the assumption that at least lowland 

 vegetation then prevailed in abundance. These carbonaceous 

 deposits have been compared in respect to the amount of carbon 

 with the coal beds of the Carboniferous and Cretaceous periods, 

 and not without some show of justice. 



There are good reasons therefore for displacing the presump- 

 tion, rather current in the earlier half of the century, that the 

 lands of the older Paleozoic periods were barren of vegetation 

 and for the substitution of the presumption that land vegetation 

 was prevalent as far back as the shore deposits display the resid- 

 uum of complete disintegration and abound in the relics of sea 

 life. Beyond that, where the schists do not radically differ in 

 chemical constitution from the igneous rocks, the era of a naked 

 earth and the reign of disaggregation with slight decomposition 

 may be placed amid the other mysteries of the Basement Com- 

 plex. 



The richness of littoral marine life, at least as early as the 

 Cambrian, the carbonaceous deposits of the Huronian and the 



