JTALY. LETTER XXVI. 327 



if any*. Then fucceeded micaceous or glimmer / 

 horn-flate, in fome parts fpotted with fekl-fpath 



and 



* No part of Mineralogy is lefs cultivated tlinn that of the 

 mountain-rocks (SaxaJ, though it be undoubtedly of great 

 importance in exacl and fcientifkal rrinera!ogicnl rbfer- 

 vations. Every defcription of a country is attended wi h 

 great difficulties ; and too often we are at a lofs for pro- 

 per exprefiions, which arifes from the want of juft claflifica- 

 tion, knowledge, and denomination of the rocks, which do 

 not generally differ but in the various mixture of their conili- 

 tuent parts. Many rocks, either compound or ferruminated 

 (Cronjied's MimraL 258.) are Hill without any name, and 

 fome others have fo many and undetermined ones, that they 

 are by no means to be underftood. For example, Granite, 

 Hornftone, Horn Hone-rock, Horr.berg, Korn-flate, Geftell- 

 fiein, are undetermined names, end for that reafon very often 

 confounded '\nd mifapplied. Granite properly confifts of 

 Qaartz, Feid-fpath, and Mica, or Glimmer; but Ibmetimes 

 the fame name is given to a rock, which contains not afirgle 

 fpark of Feld-fpath. This fpecies fnould rather be called 

 Hornberg or Hornftone-rock. If the Mica or Glimmer- 

 ftripes in it be very near one to another, fo as to make it fhi- 

 very or lamellated, it is called Geftel-llein, on account of its 

 being employed in fupport (Geftelle) of grates and fire- 

 hearths. However, it is common to apply this very name too 

 to the coarfe micaceous Hcrn-ftone rock, for want of a better 

 fpecies applied to the fame ufe. The names of Horn-itone 

 and Horn-llone rock are like wife given to fome pebble-flints 

 (pttrofelices); nay, Profeflbr Wallerius has given them to an 

 indurated clay, which in fome veins Ikirts the ore (faattand), 

 Horn-ihte is the proper denomination cf a rock, confining of 

 Y 4 Quartz 



