TRAP ROCKS. 159 



basalts of Euroj)e, except tliat they, as well as those of the 

 Stony Rid2;e, of which I shall presently speak, are decom- 

 posed miicli more readily below tiie sm lace of the ground 

 tl.an wlicn subjected to the action of the weatlier. As oxy- 

 gen is the chief, perhaps the only agent in dissolving them, 

 their iron must be in the lowest state of oxidation ; and their 

 decomposition is tliercfoie accelerated by a position, which 

 by constantly ex[)osing them to moisture, quickens the 

 change of their iron in its passage into a peroxide. But it 

 is by no means certain that their decom|)Osiiion is effected 

 exclusively byaiieans of tlie iron they contain; for tlie feld- 

 spar which is one of their constiuients, may, l)y l)eing de- 

 composed, also contribute to effect a decomposition of the 

 whole rock. When tlie ground is penetrated where the 

 rocks are most al)undant on the surface, nothing is usually 

 found hut a yellowish sand mixed with a portion of alumi- 

 nous clay, and forming a cold meagre mould of little value 

 for purposes of husl)andry. Hence it is a practice with the 

 owners of the land, who have of late l)egun to clear some 

 parts of it, to bury the rocks where they lie ; and it succeeds 

 very well. 



The (juestion respecting the origin of traj) rocks has en- 

 gaged the attention of the most celebrated geologists, and 

 it would therefore l)e presumjituous in a sciolist to attempt 

 to discuss it further than as it is directly involved in the 

 subject on which he professes to treat. I may however i)c 

 permitted to remark, that there is nothing in the position of 

 the trap of the Connewago Hills, to indicate its being igni- 

 genous. The common answer to arguments drawn from 

 the ahsenceofall tlic characteristics of a volcanic mountain, 

 to wit that the basalt was formed on the bosom of the moun- 

 tain itself, and afterwards denuded by the removal of the 

 superincumbent ma'*s, cannot be admitted here ; liecause in 

 that case we ought notto expect to find it resting on even 

 the oldest of the secondary rocks. That it may have l)een 

 deposited on the sandstone by a volcano, before the present 

 continent was elevated above the level of the sea, would be 



