CONDITIONS OF FOSSILIZATION^ 



J. CULVER HARTZELL 

 University of the Pacific, San Jose, Cal. 



Introduction. 



Superficial Consideration of Fossils. 

 Conditions in Which Fossils Occur. 

 Difficulties Encountered. 

 Authors' Definitions of Molds and Casts. 

 Definitions of Molds and Casts Followed. 

 Definitions of "Original," "Mold," and "Cast" Proposed. 

 Lithological Character of Formations, as Affecting the Preservation of Inverte- 

 brates. 

 General Character of Invertebrate Skeletons. 

 General Mineral Character of Living Invertebrates. 

 Replacing Minerals. 



Horizon, Locality, and Lithological Character of Formations Studied. 

 Minerals Replacing Original Minerals Secreted by Invertebrates. 



INTRODUCTION 



In the study of a fossil the first important point to determine is its 

 state of preservation — whether the fossil under consideration be 

 the original, a cast of the original, or a mold of the original. 



By not observing this precaution, errors have been made, and 

 will continue to be made unless it be definitely understood what 

 is meant by these terms and the conditions they represent in fossils. 



SUPERFICIAL CONSIDERATION OF FOSSILS 



A superficial consideration of a fossil is often apt to lead to a 

 misinterpretation of its condition of preservation, for fossils vary 

 in this respect. Molds may be taken for casts, and described as 

 exhibiting the external structure of the original. 



I This paper was largely prepared in 1898-99, under the direction of the late 

 Professor Charles E. Beecher, when the writer was a graduate student at Yale, and 

 was submitted for the degree of master of science. Its publication has been delayed 

 because the writer wished to collect further data, which he has done in Europe and 

 America. Another paper is in course of preparation, in which an attempt to formu- 

 late laws governing conditions of fossilization will be made. 



The writer also wishes to take this opportunity to thank Professor S. L. Penfield, 

 of Yale, for valuable suggestions during the preparation of the original manuscript. 



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