CONDITIONS O^ FOSSILIZATION 



279 



of an organism be hcllow or has a concavity, this space is considered 

 a "mold" from which a "cast" is taken. This is obviously wrong, 

 for in this case the "mold" is the object, and the "cast" the mold 

 from which a cast may be taken, and this cast will be a duplicate 

 of the object. 



Then, again, an impression from a convex object is termed by 

 some a "cast." This is also obviously wrong, for the "cast" would 

 have the markings of the object in reverse order; hence it would 

 be a mold. 



The general concavity or convexity of a surface will not deter- 

 mine it as a mold or a cast. Such determinations depend upon 

 the markings of that surface. 



DEFINITIONS OF "ORIGINAL," " MOLD, " AND "CASX" PROPOSED. 



In attempting to fix the meaning of the terms" original, " "mold," 

 and "cast," it is hoped the following definitions will prove acceptable, 

 especially the latter two: 



I. The term original is used 

 to designate an organism' that 

 has not lost its original structure 

 or composition, to any appreci- 

 able extent, in the process of 

 fossilization, except the organic 

 matter which may have filled the 

 interstitial spaces.. (See Fig. 9 a 

 and h.) 



II. The term mold is used to 

 designate the imprint of the ex- 

 terior or interior of an organism. 

 {a) If the organism leave an im- 

 print of the exterior, this imprint is a mold of the exterior. (See Fig. 10.) 

 (b) If the hollow organism become filled with material this material 



I Strictly speaking, a lifeless animal is not an organism; but in common parlance 

 the lifeless body is an organism because it is that which at one time functioned. Like- 

 wise, we speak of the products of life as organic. Therefore, for lack of a beter term 

 organism is used to denote the harder parts of animals which we term fossils, the 

 softer or destructible parts of which have decayed and passed away. The term 

 "organism" can in no sense, however, be applied to molds and casts, although 

 Ihese are fossils as much as the unaltered skeletal parts of animals. 



Fig. 9.- 

 of interior. 



-(a and &) originals; (c) mold 



