PRESERVATION OF FOSSILS 1075 



FOSSILIZATION. 



"Geologic time is continuous, and the development of life is 

 progressive. No break divides the present from the past, and the 

 geologic phenomena of the present epoch are controlled by the same 

 laws which governed those of past time. Fossilization is a mere 

 accident by which some animals and plants are preserved, and it 

 resolves itself into a process of inhumation, neither the nature 

 of the organism nor the time or mode of burial being of primary 

 significance. These are of first importance in determining the 

 degree of preservation which the fossil is to experience, and, conse- 

 quently, the nature of the record which is to remain ; but they do 

 not afi^ect the process of fossilization. which is merely the burial 

 of the dead organism. Thus the idea of change is not necessarily 

 involved in the concept of a fossil, although it is true that few. 

 organisms long remain buried without undergoing some chemical 

 change. Examples of the preservation of organisms in an almost 

 unchanged condition are nevertheless known, the most conspicuous 

 being the mammoths frozen into the mud and ice of Siberia, and 

 retaining hair, skin, and flesh intact; and the insects and other ani- 

 mals included in the amijer of the Baltic, where they have remained 

 unchanged since early Tertiary time. Ordinarily, however, the 

 flesh of the buried animal soon decays, and, consequently, no rec- 

 ord of the soft parts is retained. In plants the decay is less rapid, 

 and the buried vegetable remains may be indefinitely preserved in 

 the form of carbonaceous films. 



"The hard parts of animals are best preserved as fossils. Such 

 are the shells and other external skeletal structures secreted by a 

 variety of animals, as crustaceans, molluscs, echinoderms, corals. 

 and so forth ; and the bones, teeth, and other hard structures of 

 the vertebrates. Resides the actual remains of animals and plants, 

 any evidence of their existence, which is preserved, is commonly 

 included under the name of fossil. Thus impressions made by 

 living animals and plants in the unconsolidated rock material, and 

 structures built by animals from inorganic material, are fossils if 

 properly buried. Examples of the first are the footprints of verte- 

 brates ; the tracks and trails of jelly-fish, worms, molluscs, or 

 Crustacea ; the burrows of worms, borings of animals in stones or 

 shells, and the impression made by sea-weeds in motion. Among 

 the second class are worm tubes built of sand grains ; foraminiferal 

 shells, built of foreign particles ; flint implements and other utensils 

 of primitive man ; and the relics of the Swiss Lake dwellers . , . 



