276 



/. CULVER HARTZELL 



term "cast." He' also uses the term " histometabasis " for the 

 condition which produces a molecular replacement or substitution 

 or paramorphism.^ He uses the term "fossil pseudomorphs " 

 for the materials occupying cavities formerly occupied by shells, 

 the occupation having taken place by precipitation due to infiltra- 

 tion. He uses the term "fossil molds" for "cavities in sedimentary 



rocks which were originally 

 occupied by fossils," and 

 says that "the original sur- 

 face features and markings 

 are often minutely preserved 

 in molds." He also uses 

 the term "casts" for 

 "counter-parts of fossils," 

 and also for the material 

 which may occupy the 

 animal chamber. He 

 further speaks of making 

 "artificial casts of natural 

 molds" in order to get 

 "the original form and 

 surface features." 



Geikie^ applies the term 

 "mold" to impressions 

 made by the organism. 



Fig. y.—Michelinia clappi. (After Rominger.) To the material filling this 



"mold" he apphes the term 

 "cast." He* also applies the term "cast" to the material occupying 

 the animal chamber. 



Von Zittel^ applies the term "mold" to impressions. The term 

 "cast" he applies to the material which occupies the "interior of a 

 shell or hollow body." 



1 White, "Relation of Biological and Geological Investigations, Proceedings of 

 the U. S. N. M., Vol. XV, pp. 264-67. 



2 Dana, Text-Book of Mineralogy, (1898), p. 293. 



3 Geikie, Text-Book of Geology, 3d ed., p. 651. 



4 Geikie, Outlines of Field-Geology, 5th ed., p. 78, Fig. 14. 



5 Von Zittel, Text-Book of Palaeontology, Eastman translation. Vol. I, Part i, p. 2. 



