298 ON THE FORMATION OF ROCKS. [July, 



The word transition may not be so appropriate as 

 intermediate ; though in many situations the passage 

 from these rocks to what are called primitive, is so 

 gradual, as to render it difficult to di-aw the line of se- 

 paration. 



The application of the term transition was made by 

 those who first introduced the division, and described 

 the rocks included in it ; whereas ^^ intermediate"' has 

 been adopted without any regular classification of thft 

 ix)cks meant to be included under the denomination ; 

 from which it is probable, that in the present state of 

 our knowledge, transition being better defined, will 

 be better understood, which constitutes the principal 

 utility of all names, whether of rocks or other substan- 

 ces, 



22. Graywacke, an aggregate of small fragments or 

 particles of rocks, most frequently rounded by friction 

 or attrition ; and though not generally containing tli« 

 remains of organic matter itself, yet, as it alternates 

 with other rocks in which organic matter has been 

 found, it must be ranked by analogy as of Neptunian 

 origin. 



There are, perhaps, three species of rocks included 

 in the above ; which though united in the same kind of 

 formation, by containing particles of rocks rounded 

 by attrition, yet dijffer in the nature and relative quan- 

 tity of the cement wliich unites them, as well as in their 

 relative situation. 



The first, and perhaps the most common, is an ag- 

 gregate of different species of rounded rocks, where the 

 cement bears a small proportion to the quantity of par- 



