Igneous Origin of some Trap Rocks. 121 
of Fingal, in the island of Staffa, and the Giant’s Causeway, in the 
north of Ireland, are still more signal examples; on account of the 
regularity and height of the columns, and of their curiously jointed 
structure. The ironstone is the usual name of the common people 
for our trap, and this name has allusion, no doubt, to the dark color 
and great weight of many of the trap rocks. 
Two opinions. 
There has been much discussion among geologists on the question 
whether these rocks are of aqueous or of igneous origin. ‘The Wer- 
nerian school have maintained the former opinion, and D’Aubuisson, 
one of its ablest disciples, after writing an interesting volume* to prove 
it, was led by an examination of the ancient volcanic district of Au- 
vergne, Velay and Viverais, in France, to change his opinion. The 
Huttonian and, generally, the igneous geologists have sustained the 
opinion that the trap rocks have originated from fire; and the pro- 
gress of investigation has done much of late years to establish it. I 
was accustomed to hear these subjects discussed with great interest 
and ability, at Edinburgh, by Dr. Hope on the Huttonian and Dr. 
Murray on the Wernerian side. Prof. Playfair had also at that time 
published his Illustrations, and Dr. Murray his Comparative View. If 
J was not convinced, I was always entertained, by these learned and 
luminous teachers; but without taking sides, I reserved myself for 
opportunities of Snare observation. I used indeed, at Edinburgh, to 
see the sandstone under the trap of Salisbury Craig,} apparently hard- 
ened, as if by the action of fire; and the Huttonian challenged this 
appearance as a proof in his sei while the Wernerian claime 
that it was an alteration produced simply by drying. 
Rocky Fill. 
Trap rocks abound in this country, and the two principal ranges 
already cited, with which I am personally acquainted ; (those of New 
England and New Jersey,) repose upon sandstone, commonly con- 
sidered as the old ; but embracing, in different places, many varie- 
ties, from graytathe through conglomerate and puddingstone, to 
the micaceous and argillaceous sandstones. Junctions of different 
* D’Aubuisson on Basalt. 
t Which much resembles the East Rock at New Haven, and a two trap ridges 
maintain nearly the same position in relation to the respective to 
t As more fully described by Prof. Hitchcock, in his account of the Geology, &c. 
of the valley of the Fe Vol. VI, p. 201 of this Journal. 
Vor. XVII.—No. 1. 16 
