550 Remarks on Dr. Boase's Primary Geology. 



sition ; a class of Werner's system which for many years had fallen 

 into disuse, but has been lately revived on account of its conve- 

 nience. 



" The individuals of this calcareous series will not be treated of in 

 this place, with the exception of the magnesian rocks, serpentine, 

 euphotide, and talc-schist, which immediately follow the porphyritic 

 series. 



" The rock in contact with granite in Cornwall has been usually 

 called argillaceous schist, or clay- slate. Dr. Berger, and after him 

 many other Geologists, have termed it greywacke ; but as Professor 

 Mohs has very justly observed, it has no resemblance to this rock : 

 some have adopted the word killas, from the miners, to denote this 

 kind of slate, but have used it more vaguely than even it is done 

 provincially ; for even the miners acknowledge that some important 

 varieties of this rock are not true killas, but a kind of elvany killas. 

 The remarks of the late Rev. J. J. Conybeare are very appropriate : 

 — ' The common killas,' he observes, ' after much question as to its 

 being a variety of greywacke, which, if that term has any definite 

 meaning, it unquestionably is not, has been at last admitted on all 

 hands to be a genuine clay-slate ; but this appellation, perhaps, after 

 all, does not convey a much clearer notion of the real nature and 

 constitution of the rocks included under it, than the repudiated 

 greywacke.' In fact, no term has been more misapplied than that 

 of clay-slate ; and its application has been general to all fine slaty 

 rocks, no matter to what member of the primary slates they belong, 

 or, indeed, whether they occur in the transition or secondary classes. 

 In Cornwall, for instance, there are at least a dozen kinds of rocks 

 that are very fissile, all of which have been indiscriminately called 

 clay- slate, notwithstanding they sensibly differ from each other in 

 their external and physical character, and are respectively associated 

 with distinct suites of rocks." 



In the 5th Chapter, Dr. Boase has collected a detailed 

 description of the primary schistose rocks of other parts of the 

 world, for comparison with those of Cornwall, and remarks : 



" In attempting to shew that the primary or crystalline schists of 

 different countries are the equivalents of those of Cornwall, it is not 





