The Hanging Hills. 25 



been pushed up through fissures in the sandstone in a heated and 

 plastic condition, there is no chance for doubt. That the mass 

 was at first plastic, or of a partially molten character, is evinced 

 by the fact that on coming to the surface it often flowed away from 

 the vent in one or more directions, thus forming a kind of sheet 

 covering a considerable extent of the adjacent surface. 



And that it was heated to a high degree is evidenced by the met- 

 amorphism of the sandstone or other contiguous rock, both above 

 and below the sheet, and on either side of the rift through which 

 the mass protruded. The metamorphism or change consists some- 

 times merely in the induration of the adjacent rocks and some- 

 times in their more or less complete crystalization ; the sandstone 

 in some instances assuming a texture and hardness that make it 

 scarcely distinguishable from the trap or eruptive matter. Moreover, 

 while the trap seemed to heat the sandstone, the sandstone in turn 

 seemed to cool the trap more rapidly, and so to change it both in 

 color and texture. It is sometimes difficult to determine the pre- 

 cise line of juncture on account of the change that both kinds of 

 rock have undergone, though at the distance of a few feet, possi- 

 bly a few inches, in either direction, the distinction is very plain. 

 There are examples of contact of the trap with the sandstone exposed 

 by the recent cutting of the drives up and down East Rock, near New 

 Haven, which belongs to this same series ; also a fine example where 

 a vein of trap cuts across the sandstone at Whitneyville. Other 

 examples are described in South Hadley, Massachusetts and at 

 other points, all showing essentially the same characteristics, 

 though there are no very satisfactory exposures as yet in Meriden, 

 the broad and deep slopes of debris along the base of the cliffs 

 effectually concealing the line of contact. 



But to return to the interesting discussion of which we spoke 

 in the outset. The commonly accepted theory, as to the mode of 

 occurrence of these trap ridges, is that after the sandstone was laid 

 down — or say about the close of the Triassic period — by some pro- 

 found disturbance of the earth's crust, the whole series of rocks 

 was fractured at various points, and through the fissures thus pro- 

 duced, the trap was pushed to the surface, sometimes only filling 

 the rift like a vein and sometimes overflowing to greater or less 

 extent, and in that condition cooling and hardening and produc- 

 ing the masses as they exist to-day, except that the gradual erosion, 

 or wearing away of the softer sandstone, has served to make them 

 more and more prominent as the ages went by.* 



*We make no attempt in this paper to distinguish between the older and more 



