VARIOUS. 205 



Among the transilient rocks may also be class^- 

 ed many which are imperfect in their structure, 

 and so irregular in different portions, that they 

 embarrass the scientific inquirer. In fact, rocks 

 of this nature constitute a large portion of the 

 globe j while the specimens in cabinets chiefly 

 consist of what are called well characterised. 

 To detail and class these imperfect rocks would 

 be infinite, and uninteresting, so a few observa- 

 tions may suffice. 



Great Britain and Ireland, in particular, often imperfect and 



irregular rocks 



afford irregular and imperfect rocks. Even the of Britain, 

 granite of Scotland rarely presents the regular 

 crystallisation observable in that of some other 

 countries; consisting chiefly of felspar^ with a 

 little quartz, and remote spangles of mica. Dr. 

 Townson, in his mineralogy of Shropshire, has 

 specified many irregular rocks of this kind; 

 such as an imperfect or ill characterised granite, 

 composed of red felspar, white quartz, and 

 blackish green hornblende. But this appear- 

 ance only occurs in the most perfect specimens ; 

 while in general it may rather be called a sand- 

 stone, seemingly formed by deposition. Such is 

 also the rock of Raglith, formed of grains of fel- 

 spar and quartz, in an earthy base*. 



* Townson's Tracts, p. 163, l68, 188, &c. 



