FEATURES OF TRAP EXTRUSIONS IN NEW JERSEY 313 



trap and mud show evidences of having experienced the most violent 

 agitation. The two are mixed and kneaded in a manner so involved 

 that it can hardly be imagined. The mud has boiled through and 

 through the seething body of lava until particles of mud of every size 

 from minute specks to large masses have become incorporated in the 

 pasty flow. Both lava and mud are full of blow holes, steam vents, 

 and other forms of irregular pipes and cavities which attest the violent 

 escape of gases. 



Above this confused mixture the lava is generally found to show 

 a transition to a purer condition. It is still thoroughly vesicular for 



Fig. 9 



several feet, but less mud is found in it as we go upward. Still higher 

 no mud whatever is found, and the overlying mass of lava, probably 

 nearly seventy-five feet in thickness to the surface, is purely igneous 

 rock. The structure of this, however, is very different from the close- 

 textured rock which we found along the eastern border of the trap 

 sheet; and, in its way, the evidence of the action of escaping gases 

 and heated waters is as perfect as in the underlying portions. Amyg- 

 dules are still frequent, but the more characteristic appearance is the 

 bowlder-like structure shown in Fig. 9. The bowlders are of dense 

 trap, with crusts of dark glass. Vugs of mineral lie between, and it 

 is in these vugs that the crystallized zeolites are found. 



This structure is common throughout the whole quarry. Even 

 the masses of trap which do not show the glassy crusts or the vugs 

 are so seamed with fissures as to be easily broken apart. Toward 



