592 W. 0. CROSBY 



and thus renewed serpen tinization and the topographic relief of the 

 serpentine stock. The meager data do not permit a more detailed 

 or definite statement; but the best general conclusion appears to be 

 that throughout the Coastal Plain history the downward extension 

 of serpentinization and upward extension of the serpentine stock 

 have been active during periods of elevation and rapid erosion and 

 quiescent during periods of base-leveling and sedimentation; and 

 that, in spite of the present strong relief of the serpentine, developed 

 in large part, presumably, during the great Pleistocene elevation, 

 the successive Coastal Plain formations have been, in general, 

 deposited across the serpentine area. 



The uniformity and virtual continuity of the narrow Appala- 

 chian belt of basic magnesian stocks and possible statenliths sug- 

 gests uniformity of age or practical synchronism, the indicated age 

 being, roughly, Mid-Paleozoic, and the argument being approxi- 

 mately as cogent as for the Triassic age of the similarly homogene- 

 ous belt of basic eruptive and irruptive rocks associated with the 

 sediments of that formation. The purpose now, however, is not 

 to insist upon the precise age of the stocks of peridotite and allied 

 rocks of the ultra basic magnesian belt, but, rather, to point out 

 that in spite of similarity of composition, structure, and age, they 

 present strong contrasts in the degree or extent of serpentinization 

 and hence, presumably, of the statenlithic development. 



Recognizing that the process of serpentinization (and the same 

 is true of chloritization) belongs, in the zone of katamorphism, not 

 to the superficial and shallow belt of weathering, but to the deeper 

 and vastly more extensive belt of cementation, we realize that cli- 

 matic conditions must be eliminated as possible factors in the dif- 

 ferentiation of the stocks. Hence the fact that in the northern 

 half of the ultra-basic magnesian belt serpentinization is, super- 

 ficially at least, more general, and, as a rule, more complete than 

 in the southern half, is without climatic significance. The mean- 

 ing of this contrast, which is to a large degree regional, is not readily 

 apparent. But, whatever the initial cause of serpentinization, even 

 though we tacitly assume its beginning, in any case, as essentially 

 fortuitous or accidental, once begun this becomes a determining 

 cause of its continuance; and the change spreads through the mass 

 as a veritable mineral contagion. 



