MODE IX. AMYGDALITE. 



the term porphyroid, as admitted into the side- 

 rous division, must be restricted to such rocks as 

 have a base of siderite, basalt, or basaltin, pre- 

 senting an appearance of porphyry. Some of 

 the primitive grunsteins of Werner fall under 

 this distribution. When the base is siderous, 

 but the square crystals are barytic or calcareous, 

 &c. this denomination may also be adopted*. 

 The mixtures called granitic porphyroids, &c. 

 are to be arranged under their proper domains. 



MODE IX. AMYGDALITE. 



Where the distinctive characters of a sub- 

 stance vary much, they are omitted, to avoid 

 unnecessary prolixity, especially as they may 

 be found in the common books of mineralogy ; 

 and rocks should be studied in themselves, as 

 well as in books, for the only use of any classi- 

 fication is to assist the memory. 



This substance, the mandelstein, or almond- 

 stone of the Germans, has a base of coarse trap 

 or basal ton, in general black or brown, inter- 

 spersed with nodules or kernels of chalcedony, 

 agate, calcareous spar, zeolite, and green mag- Agates. 



* The green siderite, with crystals of calcareous spar, (Sauss. 

 \. 139, 4to.) may belong to this division. 



