various parts of Scotland, 445 



substance, and obviously mechanical structure, as the essential part 

 of the definition. I shall take an opportunity in some remarks on 

 another district, to enquire whether it would not be also convenient 

 to extend the definition so far as to permit mica slate to participate 

 with clay slate in the office of cement, the other parts of the 

 character remaining the same. 



Whatever definition be ultimately adopted, we cannot too strongly 

 inculcate the necessity of accuracy in the application of terms. 

 Accurate mineralogical knowledge is an indispensible condition to 

 accurate geological description, and the errors of very modern and 

 celebrated authors, arising from the want of this fundamental 

 quality, are too well known to call for the invidious task of pointing 

 them out. 



The cacophony of the term graywacke has excited a desire in 

 some late observers to discard it altogether, and substitute one more 

 vernacular, and less liable to that objection. 



The multiplication of synonyms is itself an evil of so crying a 

 nature, and has unfortunately become a disease of such magnitude 

 in our science, that we ought to consider well before we venture 

 to add another to the unwieldy and vexatious stock. It is so great 

 an advantage to possess one term well understood, and understood 

 as the language of philosophy should be, in all countries, that we 

 can scarcely find a motive sufficiently powerful to induce us to 

 change this received name. Under these circumstances we have 

 every reason to retain the term graywacke, however jarring to 

 English ears, and it is the excess of fastidiousness to reject on 

 account of its sound, one word from such a polyglott of unmelo- 

 dious and ill compounded Greek, French, and German terms, as 

 assail the mineralogist on every side. If there is in any case a 

 choice among equally established terms, it is in our power to chuse 



