MATERIALS 11 



" fossil " may be taken to refer to those remains or traces 

 of past life that occur in the rocks of the Earth's crust, and 

 afford biological evidence of their organic origin. The 

 last phrase in this definition excludes such phenomena 

 as beds of graphite or masses of marble which retain 

 no vestiges of organic structure, and give only pre- 

 sumptive evidence of organic origin. 



The definition shows a certain lack of precision, 

 for reasons similar to those that made limitation of the 

 scope of Palaeontology impracticable. An empty shell 

 lying on the beach, covered with sand by the wash of 

 one wave, and laid bare by the scour of the next, has 

 fulfilled the conditions required to assume the title of 

 fossil ; and the same qualifications would appertain to 

 a body exhumed by order of the Home Secretary. If 

 the shell were dug up from a prehistoric kitchen-midden, 

 or the body disinterred from a tumulus, application 

 of the term fossil would be only less inappropriate. 

 Since organic structures may remain practically un- 

 changed from very remote periods, it is useless to 

 invoke the word " petrifaction " as indicating a criterion 

 for the recognition of fossils. The ungainly phrase 

 "sub-fossil" has sometimes been applied to those 

 organic remains that occur on the border-line between 

 past and present ; but since the etymology of that 

 term is grotesque, and its scope devoid of precision 

 in both directions, its use rather aggravates the diffi- 

 culty. In practice it is convenient to exclude organisms 

 of the Holocene period from those that are called fossils, 

 but such a division is purely arbitrary, and at times 

 untenable. In some aspects of his work, a Palaeon- 

 tologist is compelled to regard himself, and the living 

 creatures that surround him, as potential fossils. 



The introduction of the word " petrifaction " into the 

 preceding paragraph demands a further definition. 



