94 Elements of Mineralogy. 



magnefia, and 6 of iron. The greenifh fort 

 contains more iron and gives a greenifh colour 

 to the nitrous acid. , 



SPECIES XL 



Argillaceous Earth intimately mixed with 4 

 times its weight of Siliceous, f its weight 

 of pure Calcareous, and fome thing more than 

 its weight of Iron. 



Toad-Jtone. 



Dr. Withering, who has given us an ana- 

 lyfis of this (lone, defcribes it as being of a 

 dark brownlfh grey colour, of a granular 

 texture, not giving fire with fteel, nor 

 effervefcing with acids : it has cavities filled 

 with chryftalized fpar : it is fufible per fe 

 in a ftrong heat. Phil. Tranf. 1782,^ p. 



333- 



100 parts of it contain 63 of filiceous 

 Earth, 14 of argillaceous, 7 of calcareous, 

 and 1 6 of dephlogifticated iron : it differs 

 but little from bafaltes ; it is fofter, contains 

 a fmaller proportion of iron, and a larger of 

 filex. 



SPECIES XIL 



