44 Dr. Heddle on the Pseitdommyhic Minerals 



This interesting pseudomorph was found at the Spindle rock, 

 where an outburst of trap tufa has passed through the lower 

 coal formation, carrying up with it and altering portions of its 

 various members : a rhomb of coal was found completely con- 

 verted into marcasite, which beautifully imitated the filaments 

 of mineral charcoal scattered through the mass. 



At Glenfarg, hollow pseudomorphic cavities of what have been 

 rhombs (/) of calcite occur in fargite, but in no instance filled 

 with any substance, the pseudomorphic change being here in- 

 complete. 



Tsle of May, in the Che's on the west side, with datholite, — 

 Prehnite after scolezite, form indistinct. 



Dumbartonshire. At the Long Craig, — 



Weissi2;ite (albite) after stilbite, forms rab; rabV; 

 rabVU: figs. 8, 9, 10. 



Fig. 8. 



Fig. 9. 



Fig. 10. 



K 



(^i3^ 



Analcime after stilbite, form rab. 

 Analcime after calcite, form y, fig. 11. 



The interior of these crystals frequently consists 

 of unaltered calcite. 



Quartz after stilbite, form rab: 

 this is, however, more of the nature of a coating 

 than a replacement of substance, as the crystals are 

 for the most part hollow. rig. 12. 



A white substance (hardness 

 about 6*, pulverulent, in- 

 soluble in acids, containing 

 silica, alumina, lime, soda, 

 and water) after stilbite in 

 the forms rab; rab M 

 (fig. 12); rabVU. 



Kg. U. 



