Ch. XIV.] OF THE STRATIFIED ROCKS. 307 



in contact with augite porphyry in the districts of the Lakes 

 Orta, Maggiore, and Lugano, as described by Von Buch : 

 dolomite is generally interposed between the limestone and 

 porphyry, but, in several instances, the limestone joins the 

 porphyry, without having experienced the metamorphosis 

 attributed to the presence of this igneous rock. 



The supporters of the Plutonic theory must often have 

 observed similar facts, but we do not know whether they have 

 made an attempt to explain how a heated mass, capable of 

 effecting such changes, could have remained in contact with 

 strata, without producing any alteration : if this subject has 

 not yet attracted their attention, it is deserving of their 

 serious consideration. In conducting this enquiry, it may be 

 suggested that the position of the igneous rock should always 

 be marked, and the precise parts, whether upper or under, 

 where the strata have been changed ; and the degree of alter- 

 ation that has taken place, in short, all particulars, should 

 be noted; for circumstances, which may often appear to the 

 enquirer minute and trivial, may be hereafter regarded as 

 very important, and tend to throw some light on this subject. 



In the mean time, it is proposed to admit, for the sake of 

 argument, that the alteration of the strata, above considered, 

 has been produced by heat; and, after having stated the 

 nature of this change, to enquire whether the metamorphoses 

 which the primary slates are supposed to have undergone are 

 analogous. 



The strata next the trap rocks are sometimes indurated, 

 assuming such an appearance as might be supposed would 

 result from a long-continued and high temperature; and 

 sometimes they appear to have been altered by a partial or total 

 fusion : thus, sandstone assumes the character of hornstone, 

 jasper, or even solid quartz: clay-slate and shales are converted 

 into flinty slate and Lydian stone, and even garnets are then 

 found which did not previously exist in the schistose rock ; 

 and secondary limestones become perfectly crystalline, their 

 organic remains at the same time disappearing, so that they 



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