I9I0.] PETRIFACTIONS AND ALTERATIONS. 19 



color, often variegated. The material has been quarried out in 

 large blocks and on the exterior these are often altered to calcite. 

 The aragonite is compact columnar massive, while the calcite is por- 

 ous, though crystalline and shows the cleavage faintly. As the cal- 

 cite retains to some extent the columnar structure of the aragonite 

 the specimens are paramorphs. Occasional calcite crystals are 

 found in cavities. Sicily furnishes excellent specimens of calcite 

 paramorphs after aragonite, but this is the first example found in 

 this country, I believe. 



9. Smithsonite after Calcite. — Granby, Missouri. This is one 

 of our best known pseudomorphs. Steep rhombohedrons of the 

 — 2R form (0221) implanted on dolomite have been replaced by a 

 spongy mass of smithsonite, but the surfaces of the crystals are 

 smooth. 



10. Smithsonite after Dolomite. — Granby, ^Missouri. A massive 

 cleavable dolomite specimen 2 cm. thick with warped rhombohedral 

 crystals on one surface have been completely changed to smithsonite 

 of a pale brown color. 



11. Cerussite after Calcite. — Granby, ^Missouri. Scalenohedral 

 (21 J i) calcite crystals of i cm. diameter are completely changed to 

 colorless cerussite with adamantine luster. 



12. Pyromorphite after Galena. — Granby, ^Missouri. Crystals 

 of ^ cm. square cross section on chert matrix consist of a little 

 unaltered galena in the center, then cerussite and finally a border 

 of green earthy pyromorphite. 



13. Calamine after Calcite. — Granby, ^Missouri. Scalenohedral 

 (2i]i) calcite crystals i cm. in diameter on chert matrix have been 

 replaced by calamine. When broken the crystals are found to be 

 hollow and calamine crystals project into the hollow center. 



14. Muscovite after Tourmaline. — Pala, California. A speci- 

 men 7 cm. long and 1.5 cm. in diameter represents an original 

 tourmaline crystal, roughly trigonal in cross-section. It is now 

 mostly white scaly muscovite in which is set a number of small 

 black tourmaline crystals in parallel position with the large crystal. 



15. Talc after Actinolite. — Apperson Creek, southeast of Sunol, 

 Alameda County, California. Gray columnar, subradiating talc is 



