OF UNSTRATIFIED ROCKS AND VEINS. 165 



a case exactly similar to that of the siliceo-calcareous 

 nodules found in trap. 



Veins of felspar and of compact felspar are not 

 uncommon in those rocks which contain veins of 

 granite and porphyry. It would be superfluous to 

 describe them particularly, as they differ in no re- 

 spect in their features from those of granite and trap. 

 It will be found that some of the veins of common 

 felspar are varieties of granite veins, as is frequently 

 indicated by occasional crystals of imbedded quartz, 

 and that the others are the bases of porphyries in 

 which the usual imbedded crystals are rare or alto- 

 gether wanting. 



It is barely necessary here to mention the existence 

 of pitchstone veins ; since, as it seems to be the only 

 form in which that rock occurs, it will be better to 

 examine the whole subject in its proper place. 



The last species of veins requiring notice, are those 

 conglomerate veins which cannot be ranked with the 

 mineral veins described in a subsequent chapter. 

 They are probably very rare, as I have met with only 

 three instances of them. In these, the materials con- 

 sist of various rounded stones with clay and sand, 

 cemented in the usual manner of conglomerate rocks ; 

 and they have evidently been formed by the casual 

 falling of the loose materials into open fissures, 



