SUCCESSION AMONG ROCKS. 271 



the mountainous districts of Aberdeenshire, it is fol- 

 lowed by quartz rock, as it is also by primary lime- 

 stone. The immediate contact of argillaceous schist 

 with granite in Cornwall, is matter of general noto- 

 riety ; and the same sequence is found in Arran, in 

 the Isle of Mann, and in Aberdeenshire. 



It may also be remarked that, in many cases, there 

 is merely an irregularity in the order of succession, 

 while, in others, one or more out of the more com- 

 mon number of the strata are absent. In the last in- 

 stance, for example, no other primary stratum than 

 the argillaceous schist, intervenes between the granite 

 and the more recent ones. 



But cases also occur, in which all the primary 

 strata are wanting. 



In Aberdeenshire, granite is found to be immediately 

 followed by the lowest sandstone of the secondary series; s/^ 

 and the same succession is found, on a very extensive 

 scale, on the eastern shore of Caithness and Suther- 

 land. It is still more remarkable, that, in the same 

 neighbourhood, there reposes immediately on granite, v-^ 

 a series containing coal, which is generally separated 

 from it by a long succession of intervening strata, 

 both primary and secondary; being that of the oolithe 

 and Lias. 



The foundation of a theory of regular succession 

 could not well be more defective; but it will be proper 

 to examine the superstructure a little. If it be common 

 to find gneiss succeeded by micaceous schist, and 

 that by argillaceous, the exceptions are so numerous 

 that the rule is of no value. In Perthshire, gneiss is 

 not only succeeded by quartz rock, but alternates 

 with it in endless succession ; while, in other places, 

 as in Shetland, it is also found forming a part of more 

 than one extensive series, in alternation with quartz 



