Igneous Origin of some Trap Rocks. 131 



i'ocks, that we can expect to find any such remarkable appearances, 

 orighiating from similar causes. 



I 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 make more precise observations upon them, I do not cite them now.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.f 



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 Edinburgh. 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 ; 

 and the 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. 



t 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 saUnc bodies, (common salt, nitrate of potash, sulphate of 

 potash, &c.) that are both fusible and soluble in water, and afford, if not crystals, at 

 least solid deposits from hoth. 



