OVERLYING ROCKS. 521 



The amygdaloids generally occur in large 

 masses ; rarely in veins. They are also, in both 

 these cases, occasionally laminar. 



The folio wing minerals are found in the no- 

 dules of amygdaloids. 



A. Siliceous Minerals. 



Chalcedony: variously coloured, zoned, and 

 striped ; onyx of lapidaries : agates. 



Cacholong : and semi opal. 



Hyalite. 



Heliotrope : a chalcedony coloured by chlo- 

 rite. 



Brown carnelian of lapidaries : a chalcedony 

 coloured by oxyde of iron. 



Chert. 



Quartz : white, transparent, or opake ; and 

 also smoky. 



Amethyst : white, transparent, or greenish, or 

 purple. 



B. Zeolitic minerals. 



Mesotype. Prehnite. 



Nadelstein. Laumonite. 



Analcime. Ichthyopthalmite, 



Stilbite. Harrnotome. 

 Chabasite. 



C. Calcareous minerals. 



Carbonat of lime. Fluor spar. 



Brown spar. Arragonite. 



Schiefer spar. 



