278 ON THE PARTICULAR ORDER OF 



what succeeds, I may refer to the Chapter on the 

 Tertiary Formations. 



Of all these groups I must now remark, that although 

 any one may be deficient, there is no instance, as it 

 is said, of the order being inverted ; but it must be 

 plain that where an arrangement approaches so much 

 to an artificial order, it would not be very easy to 

 prove an inversion. Assuming therefore certain se- 

 ries or associations, rather than individual substances, 

 the order of recurrence or superposition in the secon- 

 dary strata, is much more constant than in the primary, 

 or it, at least, appears to be so. But it must be 

 remembered that these may possess certain associa- 

 tions, or series, analogous to those of the secondary, 

 which we have not yet fully discovered, as we appear 

 to have done in the case of gneiss and hornblende 



o 



schist, but which may possibly come to light when 

 this division of rocks has been more minutely studied 

 and compared in different countries than it has yet 

 been. It is possible, for example, that the intricate 

 series of the quartz rock, and of the micaceous and 

 argillaceous schists of the Western Islands, may be a 

 characteristic and definite series, like that of the Lias 

 or the red marl in the secondary strata, and that it 

 may occur in a similar manner in other parts of 

 Europe. It is easy to see the drift of this suppo- 

 sition ; so that I need only add, that it is not a fair 

 comparison between the primary and the secondary 

 strata, when individual beds are selected for compa- 

 rison out of the one, and whole series out of the 

 other. For the present, it seems prudent to come to 

 no decision on this point, but to wait for further 

 information. It is also evident, that by omitting trap 

 in the consideration of the secondary rocks, and ad- 



