130 Igneous Origin of some Trap Rocks. 



the calcareous spar, which it embosoms ; steam and gas would of 

 course be copiously formed, and being rendered very elastic by the 

 intense heat, they would make every effort to pass upward, accord- 

 ing to statical laws ; but, the viscous and tenacious character of the 

 melted trap and of the softened sandstone would oppose great obsta- 

 cles to their free passage ; which, aided by the enormous pressure, 

 would eventually prevail, and at some distance from the surface 

 where the action of the trap upon the sandstone was going on, the ex- 

 trication and passage of the bubbles would eventually cease. The 

 sandstone, below the depth to which the heat reached, would remain 

 unaffected, and the trap, above where the elastic agents were extri- 

 cated, would be slowly consolidated, without those marks of igneous 

 action, which were derived chiefly from the nature and condition of 

 the argillaceous and calcareous sandstone. 



It is not, however, necessary to the inflation of trap, that it should 

 be in contact with sandstone or with any other particular rock ; there 

 are in the trap itself materials to afford aerial products, and whether 

 they would be evolved or not, must depend upon circumstances, 

 principally the intensity of the heat and the superincumbent pressure. 

 There are many cases of inflated traps, where we can discover no 

 immediate connexion with another rock. But in the case before us, 

 that connexion is palpable, and is coextensive with the observed phe- 

 nomena. Mr. Seymour, one of the tutors of Yale College, informs 

 me that similar appearances are common in other trap ranges in the 

 vicinity of Rocky Hill, especially in Newington, his home, where there 

 is a parallel and a higher range that has been cut through in making 

 the road, and which has been otherwise exposed in quarrying. It 

 must be remembered, that it is only where sections, derived from 

 such causes, enable us to examine die junction of trap with other 



formation that continues to Rocky Hill,) which has been used at New Haven, 

 during the two late seasons, in constructing a great building, the new State House, 

 the cavities in the rock which were entirely secluded from the atmosphere, were 

 often Ibund full of wet clay and other comminuted materials, evidentlj" the mud 

 and dust of the primitive rocks whose ruins compose this sandstone, and during its 

 deposition, accidental cavities appear to have been filled with this mud and 

 water, and then to have been closed up by the accumulation of more of the ma- 

 terials of the rock, so that the clay, wet often to the consistence of soft mortar, has 

 remained, we know not how many ages, and might have remained, we know not 

 how many more, unchanged. A mass of this mortar, which 1 carried home, and 

 worked in my hand like dough, lay in the hot air of July, for several days, before it 

 was quite dry. 



