Igneous Origin of some Trap Rocks. 131 
vocks, that we ean expect to find any such remarkable appearances, 
originating from similar causes. 
am acquainted with several places where there are junctions of 
trap with other rocks, but as I wish to examine them again, and to 
make more precise observations upon them, I do not cite them now. 
Many other junctions must be known, in various parts of the trap re- 
gions of New England, New Jersey, and other parts of this coun- 
try ; and I take the liberty to request, that those who may have it in 
their power, will make precise observations upon the appearances at 
the junctions, and transmit to me the result, accompanied by draw- 
ings and specimens when it is convenient; and at least with accurate 
descriptions.* We might thus be in a condition to form a general 
opinion of the origin of our trap rocks. Hasty generalization from 
a few facts is a great evil in science; and if there should eventually 
appear to be sufficient evidence to admit the aqueous origin of trap 
in some cases ; (as we must I think without doubt admit its igneous 
origin in many ;) we must not hesitate to go where truth and evidence, 
and sound reasoning will carry us.+ 
This caution seems the more necessary in the present case, be- 
cause there are instances in which there is apparently no direct evi- 
dence of fire, in cases where trap is in contact with other rocks. 
Such appears to be the case in the Campsie Hills in Scotland, in 
Stirlingshire, as described by Lt. Col. Imrie, in the second volume 
of the Transactions of the Wernerian Society of Edinbargh. For 
the illustration of his memoir, he has given a large and beautiful sec- 
tion, exhibiting the junction of the trap with stratified rocks below ; 
€ case is extremely similar to that of the Hartford quarry, only 
NO appearances of igneous action are mentioned, and it is fair to pre- 
sume that they would not have escaped so acute an observer as Lt. 
Col. Imrie, accustomed also as he had been to the observation of 
* Which, if permitted, shall appear in this Journal. 
| If some are disposed to say, it is absurd to admit that the same result may pro- 
ceed from opposite causes, as of fire and water, we must resort to our experience 
in order to ascertain whether there are any parallel cases; and we shall not be long 
in finding them. Camphor crystallizes from its solution in alcohol, and also from 
sublimation by heat. Boracic acid crystallizes from the mother water in which the 
borax that affords it, is decomposed by sulphuric acid; and it rises also and congeals 
in beautiful crystals from the effect of heat. Corrosive sublimate is another exam- 
ple; and there are many saline bodies, (common salt, nitrate of potash, sulphate o 
potash, &c.) that are both fusible and soluble in water, and afford, if not crystals, at 
least s¢ ' ; Z 
