OCCASIONAL ROCKS. 541 



definition of its characters will be found in the 

 proper place ; but its introduction would have 

 been indispensible, even if it had not occupied 

 so decidedly the place and presented all the true 

 properties of a rock, on account of its frequent 

 occurrence in company with siliceous schist, and 

 under circumstances in all respects identical. 



On these three rocks it may now be remarked, 

 that as they are found both in the primary and 

 secondary classes, and, in each, under slight dif- 

 ferences of character, they might have been re- 

 peated in each, as is done in the case of limestone, 

 and in that of the red sandstone. But they did 

 not appear sufficiently extensive or important to 

 demand this attention. A further reason for the 

 practice here adopted, appeared to be contained 

 in that peculiarity of position by which, as they oc- 

 cur in either of the classes, they seem to be almost 

 necessarily connected with the unstratified rocks ; 

 and to be often, in fact, portions of the ordinary 

 strata with which they are united, more or less 

 altered by the influence of those irregular and 

 intruding masses. The object of this arrange- 

 ment being to connect, as far as possible, the 



