OF UttSTRATIFIED ROCKS AND VEINS. 139 



left without a criterion to determine the relative age 

 of any independent mass of trap to the strata, as far 

 as any evidence can be deduced from mere contact. 

 It is important to rectify an error which has led to 

 the establishment of numerical and successive floetz 

 trap formations. 



The circumstances, however, under which the trap 

 rocks have actually originated and under which they 

 are displayed, render it certain that there have been 

 distinct deposits at different periods ; but it is not less 

 essential, in establishing a fact, to make use of the 

 true evidence, as the false is always in danger of mis- 

 leading or of proving too much. From the con- 

 stitution of the porphyries that accompany the older 

 rocks, it is probable that they are of a higher antiquity 

 than the traps found above the secondary strata ; but the 

 certainty of two, if not of more successive productions 

 of these rocks, is established by the same fact as it is 

 in granite, namely, by finding veins passing from one 

 mass so as to intersect another. The same is proved 

 by finding masses of trap constituting portions of the 

 conglomerate strata; but all the minute particulars 

 which relate to these appearances belong properly to 

 the history of Trap, where they will be found. 

 (Chap, xxxix.) 



On the Veins belonging to the unstratified Rocks. 



As the veins of granite and Trap are of a distinct 

 origin from the other rock veins, it will be better to 

 consider them in this place; as far at least as it is 

 necessary for the purposes of this general view of the 

 unstratified rocks. 



If veins consisting of granite or trap, have not al- 

 ways been traced to masses of these rocks, that has 



