Ch. XIV.] OF THE STRATIFIED ROCKS. 297 



effected by a mechanical transition, numerous facts clearly 

 show that the same conclusion must not be drawn ; thus, it is 

 difficult to lay down the precise line between the tertiary and 

 the secondary formations, or, indeed, between some of the 

 individual beds of their respective groups ; all of which have 

 evidently been formed at distinct periods. 



This being the case, is it at all surprising, that it is difficult 

 to separate the primary slates from the fossiliferous strata by 

 which they are immediately succeeded ? In Cornwall, a re- 

 mote portion of the calcareous series contains organic remains 

 characteristic of the oldest beds of the greywacke, or transi- 

 tion group ; and there is no point between the slates of the 

 porphyritic series in contact with the granite, and these fos- 

 siliferous beds, which can be asserted to mark the boundary 

 between these series : though, as we have stated in another 

 place, the same facilities for examination cannot be obtained 

 as are offered at the junction of the slate with granite. Now, 

 what happens in Cornwall has been frequently observed in 

 several parts of the Alps and other districts, with the excep- 

 tion of the secondary strata belonging to different groups : 

 but surely this apparent transition is no positive evidence 

 that all the rocks so connected are of the same epoch ; we 

 have said apparent transition, as we are not aware that this 

 has been actually determined by one continuous section in- 

 tersecting these rocks, and perfectly exposed to view through- 

 out its whole length. 



It has already been shown, that the conglomerates and 

 greywacke of Nare Point, Helford Harbour, in Cornwall, 

 pass by insensible degrees into the adjacent slates, from the 

 detritus of which they have been formed : and it is therefore 

 evident, that the parent slates and the derivative rocks can- 

 not have had the same origin. And the same conclusion is 

 applicable to some appearances of this kind in Caithness, 

 referred to in the last chapter. The strata of the old red 

 conglomerate have been, according to Sedgwick and Mur- 

 chison, tilted up by the protrusion of solid granite ; during 



