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of that table land, the only material generally visible upon its 

 surface, is the highly indurated and altered shale; the igneous 

 matter itself having apparently in but few instances reached the 

 day. Along the Delaware, however, about two miles above the 

 mouth of the Lookatong, and nearly opposite the mouth of the 

 Tohickon, near Black's Eddy, the trap appears on both sides 

 of the river in a somewhat massive dike. On neither side of 

 the Delaware does the trap appear at the surface on the top 

 of the ridge or table land; and would never have been exposed, 

 but for the denudation which excavated the deep channel through 

 the rocks, by which the river now flows. The existence of the 

 trap rock under these circumstances, lends confirmation to the 

 opinion already implied, that the induration of the strata in many 

 of the broad belts described, is the result in part of the heat pro- 

 pagated from masses of igneous rock which have never reached 

 the surface. 



Regarding this conclusion as almost demonstrable from the 

 phenomena, does not analogy furnish us ground for the interest- 

 ing doctrine, which attributes the crystalline structure of gneiss 

 and other stratified rocks of the primary class, io the modifying 

 influence of subjacent bodies of granitic, and other igneous matter 

 intensely heated, acting upon sandstones, slates, and similar sedi- 

 mentary strata ? 



Reviewing the several facts presented in the previous descrip- 

 tion of the principal belts of altered shale and sandstone, we find 

 many of them of a kind calculated to add weight to this hypo- 

 thesis. 



In the great thickness of the zone of strata throughout which 

 such remarkable changes have been induced in the texture, and 

 ev6n the molecular structure of the rock, by the heated trap, we 

 have evidence of the magnitude of that cause, which when exerted 

 in far greater intensity and universality upon the sedimentary 

 deposits of the earlier periods of our planet, may have been fully 

 adequate to produce that more entire change to general crystalli- 

 zation, which the metamorphic theory assumes. A curious and 

 important proof that the modifications in the strata described, 

 have resulted wholly from the high temperature of the molten 

 trap, is to be found in the circumstance that all the indications 

 of alteration or an approach to a semifusion of the mass, augment 



