382 NATURE AND CHARACTERS 



precise line at which the boundary between the 

 primary and secondary classes was drawn : why 

 the red sandstone was considered the first of the 

 secondary series. That enquiry is more particu- 

 larly connected with the present remarks ; as 

 the leading distinction of this rock, namely, the 

 mechanical structure, forms one of the chief cha- 

 racters of the secondary strata. 



It has been remarked, that where the primary 

 and the secondary strata are found in contact, the 

 latter do not always follow in parallel order to 

 the former, but rather meet them at some angle. 

 Moreover, in thus meeting, the surfaces of the 

 secondary strata are sometimes found lying on 

 the edges of the primary, as was formerly men- 

 tioned in treating of the distinctive general cha- 

 racters of rocks. To this position, as already 

 remarked, the terms unconformable and over- 

 lying have been applied, arid it has been enu- 

 merated among the necessary distinctions be- 

 tween the primary and secondary strata. But, 

 like all the other characters of these latter rocks, 

 this one is by no means universal, and we must 

 beware of erecting from it a general rule, as it is 



