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- 
irication 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 Roeky 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 the junction of trap with other 
formation that continues to Rocky Hill,) which has been used at New Haven, 
during the two late seasons, in coustructing a great building, the new State House, 
the cavities in the rock which were entirely secluded from the atmosphere, were 
often found full of wet clay and other comminuted materials, evidently the mud 
and dust of the primitive rocks whose ruins compose 
ze nein oe sea aR A inass of this mortar, which I carried home, and 
‘Worked in my hand like dough, lay in the hot air of J bik 
wasquitedry. ar of July, for several days, before 
