I9I0.] PETRIFACTIONS AND ALTERATIONS. 21 



district are molds or cavities from which the calcareous matter has 

 been dissolved out. The specimen described is a cast probably 

 formed by filling of the mold and not by direct replacement of the 

 organism. 



19. Pyrite replacing Aviculopccten. — Leavenworth, Kansas. 

 Some excellent pyrite petrifactions were obtained from the Chero- 

 kee shales on coal mine dumps at this locality. The pyrite is bright 

 brassy with purplish tarnish. The fossil is Aviciilopecten rectila- 

 tcrarins, which, in Kansas, is limited to this horizon. 



20. Liiiwiiite replacing gasteropod. — Carnegie, Corral Hollow, 

 California. Fossils of fresh-water gasteropods (probably a new 

 species of Melanea according to Mr. Harold Hannibal) occur in 

 Eocene sandstone exposed along the railroad track near Carnegie, 

 San Joaquin County, California. The sandstone is composed of 

 quartz grains with limonite cement. The shells are completely re- 

 placed by dense limonite .5 mm. thick. 



21. Limonite replacing twigs. — Bingham, Utah. In Upper 

 Bingham Canyon along the creek bed are found specimens of a por- 

 ous mass of soft, earthy limonite. These evidently represent 

 former plants as hollow, flattened stems are plainly visible. 



22. Malachite replacing cedar ivood. — Bingham, Utah. At the 

 locality mentioned above, malachite with structure of the cedar 

 wood common at the same place occurs. The mineral is porous and 

 often has a mammillary surface in free spaces. The cell structure 

 of the wood is visible with a hand lens. Selected pieces are com- 

 pletely soluble in hydrochloric acid showing complete replacement 

 but in other cases there is simply a thin green coating of malachite. 



23. Barite replacing Prodiictus. — Elmont, Kansas. The writer 

 is indebted to Dr. J. W. Beede for this specimen. A specimen of 

 the brachiopod shell, Prodnctus punctatus, has been completely re- 

 placed by pink barite and the surface markings characteristic of 

 this species are preserved. A visit to the locality which is a lime- 

 stone ledge two miles northwest of Elmont, Jackson County, 

 Kansas, revealed a number of fossil pelecypods and gasteropods 

 partially replaced by pink barite, but none so complete as the one 

 described. 



