various parts of Scotland* 449 



other respects preserving a perfect graywacke character, and being 

 composed of distinctly rounded as well as crystallized grains of 

 quartz, joined by a common cement. 



It is plain that there will be a point of gradation where it will be 

 impossible to say to which of the two the rock in question ought to 

 be referred, although the extremes are perfectly characterized, in 

 the one case by the laminar form of the quartz and mica, in the 

 other by its granular disposition. I shall not be surprised if future 

 observers discover that the rocks of the graywacke structure alter- 

 nate here with those of the micaceous schist. Should this be the 

 case, it will confirm the supposition which I have suggested in 

 other parts of these papers, that no real and well defined line of 

 distinction exists between the transition and primitive rocks, but 

 that they form a graduating series of one single formation ; a series 

 so gradual as to render it expedient once more to return to the 

 most simple divisiori of rocks, into primary and secondary. 



Vol. II. 3 L 



