Igneous Origin of some Trap Rocks. 12T 



pearance that has been described, and it extends up much higher than 

 in the general mass, and is visible for some distance inward, from the 

 contiguous surfaces of the masses of rock, penetrating into their sub- 

 stance. In a few places, the inflation of the trap rock continues high- 

 er than has been described in the general statement ; it seems as if 

 the force which produced the effect, suddenly hove up a wave, until 

 it was repressed by superincumbent pressure, and again subsided to 

 the general level. Perhaps it would imply too much of hypothesis, 

 if we were to say that this arose from the mass above being less 

 heavy, as the superincumbent trap appeared in such places generally 

 thinner ; but it was not always so in appearance, for there were 

 places where the trap was only a few feet in thickness, and the in- 

 flation was not always increased.* 



What is the impression which these remarkable appearances must 

 make upon a common mind of good intelligence ? Some of the spe- 

 cimens, both of the altered sandstones and traps, were exhibited to 

 such persons, and without imparting to them any hint of their suppos- 

 ed origin, they were asked what gave those stones that appearance ? 

 the answer was, they have been in a furnace, and the different va- 

 rieties have been subjected to different degrees of heat. 



Such are the impressions of all who view the specimens, and it is 

 decisive that they are of a very indubitable character, because all agree 

 in their opinion of them, whether interested in such subjects,f or in- 

 formed in geological facts and theories, or not. For myself, I must 

 say, that the eftects that have been produced, both upon the trap and 

 sandstone, which are so distinctly and strikingly visible for an average 

 depth of seven or eight feet, and in some places more, and for a 

 continued distance of nearly a mile, are such as I can attribute to no 

 agent but fire. That there was a great and pervading cause, which 

 operated upon both rocks at their junction, cannot be doubted ; that 

 this cause was resident in the trap, seems almost equally certain, be- 



^ It does by no means, however, IblloWj that this was the original condition of the 

 trap ; the contrary is perhaps hiofhly probable : that is to say, that there was origi- 

 nally a much thicker mass, either of trap or other matter, above the whole of that 

 which we now see, and that in the progress of ages, it has been removed by the 

 operation of both gradual and violent causes. 



t Inrny last visit to this place, I was in company with several highly intelligent 

 gentlemen, and in a former one, with ladies of a similar character, and the impres- 

 sion made upon them all_. was the same.' I found it' even among the workmen iu 

 the quarry, 



