Site of the Ancient City of the Aurunci. 225 



factory for those who adopt such a theory, to be able to jus- 

 tify their belief in it, by pointing out facts, which, like the 

 experimenta crucis in chemistry, seem irreconcilable with any 

 other hypothesis. 



Of this description, as it appears to me, is the protrusion 

 of a compact mass of trachytic rock through the centre of a 

 mountain mainly consisting of materials so different from it, 

 as leucitic porphyry and volcanic tuff; and its attaining, 

 moreover, a height so considerable, as it has done, in the in- 

 stance before us. 



The first difficulty in the way of supposing it formed by 

 the same operations as those which produced the mass of the 

 surrounding mountain, arises from the constitution of its com- 

 ponent parts, whi<}h is such as to imply a different origin for 

 the two. Moreover, it may be remarked, that if the Monte 

 della Croce had consisted of heaps of incoherent scoriae, or of 

 large fragments of slaggy lava piled one above the other, 

 like the cone which is now forming in the centre of the crater 

 of Vesuvius, its existence might then, indeed, have been ex- 

 plicable by an appeal to the everyday operations of which we 

 are eyewitnesses in volcanoes now in activity. 



Had it even formed part of a stream of lava, which might 

 still be traced down the external flanks of the mountain, al- 

 though we should have wondered at its ample dimensions, we 

 might, nevertheless, have referred it to the same cause ; but 

 a conical mass of rock so considerable, and yet so completely 

 circumscribed within the area of the crater, could only, as it 

 would seem, have been brought into the position which it is 

 seen to occupy, by being upheaved all at once from the inte- 

 rior of the globe, whilst in a semi-fluid or pasty state, but 

 not in a condition of actual liquidity. 



We have, therefore, before us an agent, which would not 

 only be competent to uplift the surrounding strata of tuff, but 

 which must necessarily have done so, if the latter had been, 

 at the time of its eruption, in an horizontal position ; and to 

 suppose them gradually formed by successive showers of loose 

 incoherent ejected materials, before the trachytic rock in its 

 centre was protruded, seems to imply a forgetfulness of the 



