300 EXAMINATION OF A CALCAREOUS STONE. 



Granitoid of The examination of various greenstones of the basaltic 

 eisuer. mountains of Germany, of the granitoid of mount Meisner 



among others, had formerly led me to a similar conclusion, 

 and I perceive with satisfaction, that certain greenstones of 

 Cantal indicate a similar formation. This however does not 

 prove, that there are no basaltes composed of the elements of 

 feldspar and augite confusedly united, much in the same 

 manner as we see certain porphyries with base of petrosilex 

 are nothing but compact sienites, or formed of feldspar and 

 amphibole; while others are compact granites, or formed of 

 the elements of feldspar, quartz, and mica. 

 Augite former- The author of the letter finds it difficult to conceive, how 

 withTmphi- ^'^ those, who have written on mount Meisner, should have 

 bole. been deceived respecting its coinposition. I will show how 



we may readily account for this. Formerly the- augite was 

 considered merely as a variety of amphibole (hornblende). 

 Werner was the first, at least in Germany, who distinguished 

 these two substances, which in many respects resemble eacli 

 other; but he did not distinguish them till after he had 

 written on mount Meisner, and said, that the granitoid on 

 the summit of that mountain was composed of feldspar and 

 amphibole. Authors have since repeated this assertion, and 

 continued to give the name of amphibole to what is in reality 

 augite. I have pointed out a mistake of this kind some 

 years ago; and I have lately mentioned, that part of what 

 some persons, myself among others, had taken for amphi- 

 bole, in mount Meisner, was partly feldspar coloured green, 

 and partly augite ; but I did not go so far as to assert, that 

 this rock contains no amphibole. 



XI. 



An Examination of a Stone of the Calcareous Species called 

 *' Thunder Pick." By Mr. J. ActoNj of Ipswich. Com- 

 municated by the Author, 



Common A HE great eagerness, with which newly discovered and 



much neglect- ^^^^ minerals have been sought after by men of science in 

 ed« order to their analysis, has occasioned the more common ones 



to 



