78 THE TRAP FORMATION OF 



lias, disguised, and displaced when the trap was erupted, or by that ex- 

 plosive power and plutonic heat, which glazed and hardened the sand- 

 stone rock.* 



As to the trap it is here a very extensive deposit, though still but 

 part of a whole. All its rocks are basalt, or matter of near alliance with 

 it, and composed principally of hornblende and felspar in an earthy state. 

 It is altogether an earthy deposit ; varieties of green-stone, or basalt, or 

 any rocks of a distinct crystalline texture are wholly wanting, and by 

 such deficiency so many others of the trappean list are equally, it would 

 seem, not to be found ; and the idea obtrudes, whether the circumstance 

 of a simple mineral, like this sand-stone described, being the including 

 rock, or basin, has not debarred complexity, and preserved to the trap 

 singleness of feature and texture, and manner of being. The color of the 

 harder basalt is either greyish black, or jet, and that of the softest kindred 

 clay mottled greenish grey ; and all other varieties, as to induration or 

 complexition, vary between these extremes. In the hills, the indurated 

 masses have mostly their angles rounded, and appear heaped up together 

 with a variable proportion of wacke clay, added to which, there will be seen 

 frequently, a patch or lime-stone stratum, occurring nearest the base. 

 The base of the hills is invariably broader than the summit, and, if the 

 sides of a hill are smooth and even, balled trap or basalt, often a concen- 

 tric lamellar variety, will be the principal component matter, decomposing 

 and decomposed into a predominating workable clay, still shewing the 

 parallel converging layers. The smaller vallies appear much scooped, or 



concave. 



* The first noticing of the peculiarities of the lime-stone is due to Captain Franklin, and the 

 idea of the oolites and chalk is given nearly in his own words — but I am responsible for hazarding 

 publicity. 



