OVERLYING ROCKS. 467 



pecting their possible relation in point of time tp 

 the rocks of the primary and secondary classes, 

 it only remains to describe the geological con- 

 nections in which they actually occur. That 

 they frequently rest on the most antient primary 

 rocks, or that they send veins through them, is 

 no proof, as already shown, of a connection in 

 point of time; as the same effects would take 

 place, although a deposit of this nature were to 

 be formed at the present moment. 



They have been found in contact with every 

 rock, from granite, upwards, to some of the most 

 recent of the secondary strata. It is yet however 

 uncertain, whether there are masses of these 

 rocks later than the whole of those strata ; and, 

 more particularly, it remains to be proved, whe- 

 ther any such formation has taken place since the 

 deposition of the fresh-water series. As far as 

 relates to their antiquity, when compared to the 

 different members of the secondary class, there is 

 precisely the same difficulty as that stated in the 

 last paragraph : so that we must be content to 

 suppose them posterior to the whole, merely for 

 want of proof to the contrary. This remark, 

 H n 2 



