C. II. White — Autophytography. 231 



Art. XX. — Axitophytography : A Process of Plant Fos- 

 sitization >y by Charles Henry White. 



The evidence for the existence of plant life on the earth in 

 past geological ages is both direct and indirect. We may 

 include in the class of direct evidence all the records of vege- 

 table life in which the form or structure of the plant is in any 

 degree preserved, and in the class of indirect evidence, such as 

 offer no clew to plant form, but merely indicate in a second- 

 ary way, the existence of vegetable life. In this latter class 

 are coal and certain deposits of calcareous and siliceous sinters 

 and bog-iron-ore. The plant records to which attention is espe- 

 cially directed in this paper may be placed in the category 

 of direct evidence, since the trace or outline of the plant is 

 distinctly preserved ; but the process by which the outline 

 is recorded in the rocks is wholly different from those processes 

 to which the formation of plant records is usually attributed. 



The ways usually described by which the plant form is 

 recorded in the rocks may be included in the following three 

 classes. The first class includes those in which the original 

 substance, or tissue, of the plant is, in part at least, preserved. 

 Such remains are often found within, or in close association 

 with, deposits of shale, peat, coal, diatomaceous earth, and 

 the like. The second class of records by which the form is 

 preserved is that in which the plant tissues have been removed 

 by decay or otherwise, leaving only the impress or mould as 

 the record in the rocks. The third class is that in which the 

 mould has been filled by a cast, either after the complete 

 removal of the plant, or by a gradual so-called molecular replace- 

 ment. 



By the process of plant fossilization here described, the 

 plant undergoing decomposition reproduces itself in outline on 

 the rock surface upon which it rests, or upon the matrix within 

 which it is enclosed, either by the precipitation of colored 

 mineral matter, or by the alteration or removal of the coloring 

 matter already in the rock. In the first of these processes the 

 rock surface receives a deposit of colored mineral matter, a 

 positive picture, — to borrow the language of the photographer, — 

 is nrnde (see figures 1 and 2) ; and in the second, the uniform 

 coloring matter already in the rock is abstracted where the 

 plant, during growth or decay, has been in contact with it, 

 giving a plant picture in lighter color, a negative (figures 3 

 and 4). For such plant pictures, or plant writings, in which 

 the traces or outlines of plants are distinguishable by their 

 color, and in which the variation of color from the matrix is 

 due to chemical change brought about by the plant reproduced, 



