Junction of Trap and Sandstone. 107 



but whether it is a dyke or an overlying mass, is not very easy to de- 

 termine. Another mass similarly situated reaches from the main 

 dyke at the west bank of the stream, and may be either a dyke, or 

 superincumbent mass. The sides of the dyke are irregular, not pre- 

 senting the uniformity of width and fracture, which we should expect 

 in a seam, arising, either from desiccation or refrigeration; but rather 

 the appearances we should suppose would result from a violent disrup- 

 tion of the strata. There are several small veins, ramifying from the 

 principal dyke, when a fracture or breach in the sandstone offered 

 a place for its introduction, presenting such appearances as would 

 result from filling a shattered wall of huge brick with melted lava, 

 affording, it would seem indubitable evidence of its igneous origin. 

 The junction of the two rocks affords no less striking proof of the 

 existence of an intense heat. The sandstone, at the junction of the 

 two rocks, appears to have been fused, and although where the veins 

 are extremely narrow, the sandstone is unchanged at the distance of 

 an inch from the dyke, yet when the dyke stretches to a considera- 

 ble width, the two rocks are so thoroughly incorporated, as to render 

 it impossible to decide where one rock ends, and where the other 

 begins; and although in the distance of two feet, one is a hard fine 

 grained trap, and the other a coarse sandstone, the transition is so 

 gradual as to defy the most accurate observations of the most expe- 

 rienced observer to point out any precise line of demarcation be- 

 tween them. 



Fragments of sandstone disengaged from the strata to which it for- 

 merly belonged, are imbedded in the trap, and seem to have been 

 most thoroughly baked ; are harder than sandstone in places opera- 

 ted upon by the rains, frost, and atmosphere ; have lost, in many in- 

 stances, much, and in some instances, most of the redness of color, 

 and present the same fused edges, and gradual passage into trap, as 

 do the edges of the strata before described. 



Another mass or fragment of sandstone torn from its original bed, 

 and resting on trap, may be seen in ridge No. 9, fig. I. on the road 

 leading from Wallingford to Northford, about two miles south east 

 from the center of the former place. The ridge of trap rises at an 

 angle of about 70°, to the height of from fifty to sixty feet above the 

 sandstone which appears at its base, and near the top of this ridge 

 of trap, and surrounded by it on all sides except the front, lies a huge 

 fragment of sandstone near twelve feet square. 



