Maclure on the Arrangement and Origin of Rocks. 263 



vently alternating with the transition class, though their 

 relative position, from the smallness of the mass, exposed 

 by the decomposition of the superincumbent transition, 

 cannot be so easily ascertained. Col. Silvertope lately 

 discovered a small conical hill, rising from under the 

 transition limestone, near Orihuela, of which he gave me 

 specimens, which called to my recollection other locali- 

 ties where I discovered the same order of superposition ; 

 from which it would appear probable that the active 

 agents of fire and water have been, alternately and suc- 

 cessively occupied, in forming all kinds of rocks, above the 

 primitive ; and what tradition or historic page can contra- 

 dict the supposition, that the same two or more active 

 similar agents may not have been alternately and succes- 

 sively employed in forming all that we can see of the 

 primitive rocks ; that some agent similar to fire has formed 

 the porphyries, sienites, hornblende rocks and granite, 

 and some unknown agent resembling water, may have 

 made and aggregated the rest of the primitive rocks. 

 When we gaze through our largest magnifying telescopes, 

 at the expanse of the heavens, or look into the past and 

 dream of eternity ; on considering the small atom of space 

 or time that exact observation has occupied, we must 

 be convinced that we have no right to limit either, nor to 

 estimate with our lilliputian senses the operations of na- 

 ture. All compact lavas are smooth and unctuous, losing 

 great partof their characteristic roughness, even those full of 

 small imperceptible pores, which in their fresh state con- 

 stitute that harsh feel, which serves to distinguish volcanic 

 rocks ; through time and exposure to the elements all those 

 small pores, as well as the large ones, are filled by depo- 

 sitions, and put on the appearance of that smooth unctu- 

 ous fracture, so common to Neptunian rocks. From this 

 it appears probable that lavas lose their distinguishing 

 marks and approach nearer the state of Neptunian rocks 

 in proportion to their age, and to the length of time they 

 have been exposed to the action of the elements. One 

 has onl)'^ to examine any current of lava which has been 

 for some thousand years exposed to the action of the 

 air, to find the water has filtered by the impercep- 

 tible pores to the very centre, of the apparently solid 

 rock. I first discovered this fact near Montpelier and 

 have since remarked it in different places. It is there- 

 fore possible that a Java with small pores imperceptible to 



