OF UNSTRATIFIED ROCKS AND VEINS. 147 



stated. Nor is trap exclusively superficial ; since it 

 is actually found beneath the strata in considerable 

 masses, or else in such a relative position to them 

 vertically, as to resemble granite in this respect; 

 while, it will further be shown hereafter, that many 

 of the extensive masses of these rocks now visible 

 at the surface, have actually been once covered by 

 strata which have disappeared in the progress of decay. 

 It would be an obvious, yet a superficial conclusion, 

 that the trap rocks have been deposited, like the ac- 

 companying strata, from above. But the moment 

 that their igneous origin is admitted, that opinion 

 falls to the ground; as there is no external source 

 whence they could have been derived. By the ar- 

 gument of dilemma therefore, we must seek their 

 origin in the same regions that produced granite. 

 That this really is their origin, is further proved by 

 the positive arguments derived from the masses that 

 lie beneath or among the strata, by the depth and 

 magnitude of their veins, and by the marks of force 

 which accompany their juxtaposition to the strata. 

 If any further doubt could exist, it would be removed 

 by the phenomena of volcanoes. The substances 

 which these produce are not only strictly analogous 

 in all their essential characters to some of the trap 

 rocks, but often undistinguishable ; while the varia- 

 tions which do appear, admit of an easy explanation, 

 from differences easily defined. These rocks, having 

 passed through the strata, flow over them in certain 

 cases ; while, in many others, there is reason to sup- 

 pose, from the effects following the earthquakes which 

 accompany them, that they have intruded among the 

 strata beneath the surface, so as to have produced 

 those well-known permanent elevations of the land 

 found in volcanic countries. That they elevate the 



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