Ch. XII.] NATURE OF STRATIFICATION. 243 



view have a corresponding, though perhaps somewhat varied, 

 constitution. Again, in the granite of the Land's End dis- 

 trict, though the rocks assume a different character, yet here 

 also occur various alternations of shorlaceous, common, por- 

 phyritic, pinitic, and other kinds of granite, with several 

 kinds of felspar porphyry. Nor must it be omitted to men- 

 tion, that this series, as well as that of every other granitic 

 group in Cornwall, is augmented by the frequent presence of 

 a rock which would be called by Macculloch quartz-rock ; it 

 is sometimes nearly pure quartz of different tints, sometimes 

 it is more granular, and is combined with mica or with talc, 

 which occur in every proportion, from the smallest quantity 

 till they equal or exceed the quartz. Here, then, we have 

 what is commonly considered as a stratified rock, entering 

 into the series of unstratified formations : nor is this peculiar 

 to Cornwall ; it has been noticed in Ireland, in Scotland, and 

 in other countries, as detailed in the third chapter. In Scot- 

 land, Macculloch* found the granite near Glen Tilt accom- 

 panied by, and in connection with, quartz-rock, along the 

 whole ridge of Grianan, and in the elevated hills of Cairn 

 na' Chlavhan and Connalach More: and he endeavours to 

 account for this apparent anomaly, by attributing the pre- 

 sence of the quartz-rock in these situations to superficial and 

 persistent masses, which escaped the common wreck of the 

 strata by which the whole granite is supposed to have been 

 once covered. He would not, however, have offered this 

 solution, had he enjoyed the superior advantages which Corn- 

 wall affords for investigating this phenomenon : for there, the 

 extended sections which are exhibited by the cliffs, and by 

 mining operations, have taught us that the quartzose rocks 

 not only pass into the adjacent varieties of granite by mineral 

 gradations, but that they extend to great depths, and con- 

 tinue their course longitudinally, for a considerable distance. 



* Geol, Trans., vol. iii. p. 296. 

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