222 



object it is to investigate those circumstances, 

 rather than to collect specimens for a cabinet. 

 As in all the other instances of this species of 

 uncertainty, these rocks are noticed in the cata- 

 logues, under the several heads where they occur* 



Gneiss, micaceous schist, chlorite schist, 

 talcose schist, hornblende schist, actinolite schist, 

 and serpentine, have no copies or counterparts 

 in the secondary class, and therefore require no 

 observations. The case of serpentine connected 

 with trap veins, is too rare, and, at the same time, 

 too obvious, where it does occur, to require any 

 caution. 



Between some varieties of quartz rock and 

 the secondary sandstones, there is an occasional 

 resemblance ; as the former may present a loose 

 texture, and the latter an indurated one : in such 

 cases, as in that of granite, recourse must be had 

 to the geological connections of the rocks in doubt. 



The same remark, even in a greater degree, 

 applies to the primary and secondary red sand- 

 stones, which often bear a very exact resem- 

 blance, both in compositior and general aspect. 

 It is true, that the primary rock is characterized 



