282 Prof. J. D. Dana on some Results of 



plutonic and volcanic rocks proceed, and which allows of the 

 movements observed in the solid crust." 



It will be perceived that the hypothetical viscous layer of 

 Hunt lies between a rind made out of sedimentary formations 

 and a solid nucleus which is at surface of sedimentary origin ; ' 

 and the viscous layer which Professor Hopkins regards as be- 

 longing to a stage in the process of solidification is supposed to 

 have been closed up, or some way put hors de combat. 



This substitution appears to be quite unnecessary, and the 

 process incapable of producing the result claimed. As has been 

 already explained*, the pressure from the gravitation of sedi- 

 ments cannot produce the heat needed for the fusion, any more 

 than it can cause the plications alleged to attend it. If, then, 

 no fusion of sediments would have resulted from such a cause, 

 there was no chance for the formation of the deep and extended 

 plastic zone required to meet the demands of the grand system 

 of oscillations the earth's surface has experienced. In fact the 

 conditions Professor Hunt's hypothesis appeals to (that is, thick 

 sedimentary accumulations, such as those of the Appalachian 

 region) are far too local for the production of so vast a plastic 

 zone, even if fusion were a possible result of the accumula- 

 tion. 



Again, the facts mentioned on the preceding page give as 

 positive a declaration against this origin of the material of ig- 

 neous ejections through the fusion of sediments. The sedimen- 

 tary strata along the Atlantic border, whether unaltered or 

 metamorphic, deep-seated or superficial, vary every score of 

 miles, and could not yield a uniform quality of fused material 

 for the ejections. In the Connecticut valley the metamorphic 

 rocks from New Haven, Conn., to Northern Massachusetts, a 

 distance of a hundred miles, have an east-north-east strike ob- 

 liquely across the region of trap -ejections, and are on the west 

 side chloritic mica-slate, diabase, chlorite slate, argillite, mica- 

 schist, gneiss, and other micaceous rocks of various kinds ; and 

 the Archaean (Azoic) rocks to the west in Dutchess Co., N. Y., 

 and in Connecticut west of Winsted, are diverse varieties of 

 gneiss and granitoid gneiss, containing orthoclase and albite or 

 oligoclase with quartz, and sometimes hornblendic, but, as far 

 as known, without Labradorite. Only wide diversity, not uni- 

 formity, could come from such varied material. Dolerite is, 

 moreover, the last rock to be looked for from any of it, except 

 it be from the diabase. For it has a low percentage of silica 

 (46 to 52 per cent.) and no free quartz, with 8 to 12 per cent. 

 of oxide of iron, about as much of lime and also of magnesia 



* Supra, page 217. 



