38 DESCRIPTION OF THE PRIMARY [Ch. IV. 



but abound much more in greenstone, especially its obscurer 

 varieties, and in dark-coloured limestones ; sparingly metal- 

 liferous, containing no tin, but productive of lead and anti- 

 mony ; and lastly, possessing occasionally organic remains. 



Most of the rocks of the calcareous series appear to be 

 referrible to the older portion of that class which is interme- 

 diate between the primary and the secondary, commonly 

 known by the name of transition ; a class of Werner's system 

 which for many years had fallen into disuse, but has been 

 lately revived on account of its convenience. 



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 n 

 resemblance to this rock : some have adopted the word killai 

 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 



