644 



ADDITIONS AND CORRECTIONS. 



DIALLAGE ROCK. 



WHEN the preceding pages were written, and 

 indeed until the greater part had been printed, I 

 had no practical knowledge of the geological con- 

 nections of diallage rock, and was unable to pro- 

 cure any accurate information respecting it. I 

 was therefore compelled to leave it as a subject 

 for future correction ; but it was enumerated at 

 the end of the article on Granite, as I had been 

 informed by an observer that it was an unstrati- 

 fied rock, and that it belonged to the primary 

 class. The nature of its composition seemed to 

 claim that as its most probable place. 



Having, since that period, had an opportunity 



of examining it in Shetland, where it forms an 



extensive tract, the following description, drawn 



, from its characters in that country, is subjoined. 



