THE SCHISTOSE ISLES. 



6. Hornblende schist with mica. 



7. The same with grains of green compact felspar inter- 

 spersed. 



applied. I am aware that the term primitive greenstone has sometimes 

 been applied to similar rocks, but the confusion created by its use is 

 considerable ; since, according to the views of many geologists, the trap 

 rocks, even when in the form of veins, or in other respects of an 

 obviously later date than the stratified rocks in question ; have also been 

 distinguished by the same name; from the mere circumstance of a 

 position which must in such a case be considered accidental. In these 

 instances the adjective term, primitive, becomes fallacious; tending 

 to increase a confusion which is already very inconvenient and injurious. 

 Until that confusion shall be remedied by a more comprehensive and 

 precise nomenclature, descriptions unaccompanied by specimens and 

 drawings, will frequently be unintelligible. To prevent such mistakes, 

 in the present dearth, and under the present ambiguity of terms, no 

 method remains but the circuitous explanation here adopted. I am 

 equally aware that the term hornblende schist is not universally applied 

 to the schistose mixture of felspar and hornblende above described. In 

 strictness it is only applicable to a schistose arrangement of simple horn- 

 blende. The term greenstone schist has been used for this rock ; but it 

 has also been applied to other schistose substances of different charac- 

 ters; for which reason it is prudent to avoid it, as well as all other 

 terms, which, having been originally used in an ambiguous sense, can 

 scarcely ever be limited afterwards. It is an additional objection to the 

 use of the term greenstone, that having been most commonly applied to 

 the rocks of the trap family, it is apt to excite associations which it is 

 desirable to avoid. 



Till more mineralogical names are invented, so as to distinguish effec- 

 tually all the compound rocks, it appears stilt preferable, in descriptions 

 of a country, where the leading objects are of a geological nature, to use 

 such general terms as shall obviate any chance of misleading the reader 

 respecting ;the affinities and positions of the rocks described, The 

 ambiguity that might arise from them is prevented by describ- 

 ing the specimens ; and thus the sense in which the term is used will 

 always be understood, since the definition will accompany it whenever 

 that appears necessary. To illustrate further these remarks, I may refer 

 to a rock also occurring here, which, under one general and received term, 

 includes many substances differing from each other more than the mixtures 

 of hornblende and felspar do from common hornblende schist : namely, 

 chlorite slate. This may consist of simple schistose chlorite, or of 



