METHODS OF PRESERVATION 11 



that in a geological sense they were for the most part short lived 

 features and that the bulk of the earth's surface has been for- 

 ested until modern times . . 



The agents of fossilization have been and are streams, lakes, 

 lagoons and seas. A constant shower of life falls on the bosom of 

 the waters. Trees have their roots undermined by erosion and 

 topple bodily into the streams; leaves, fruits and sticks make up a 

 large percentage of the river drift. This river drift may travel 

 near or far, much of it rots beyond recognition, but always some- 

 thing is saved. Logs and branches are stranded and buried in 

 river bars where some become petrified. Leaves and fruits become 

 water logged and sink in slack waters where they are covered with 

 mud, or the forest htter on bottom lands may be spread with a 

 mantle of alluvial mud during periods of high water and thus be 

 preserved. Anyone who has seen the variety of leaves and fruits 

 that streams are constantly carrying in our own country or the 

 vast amount of vegetable drift in such estuaries as the Guayaquil, 

 the Amazon or the Orinoco cannot doubt that the present is pre- 

 serving its records for the future or that the past similarly has not 

 failed us. The forests near the coast contribute like things to the 

 bayous, estuaries and lagoons or carry a part out to sea, and the 

 same processes are taking place around all the innumerable lakes 

 and ponds. 



The actual methods of preservation are divided into two cate- 

 gories — one termed infiltration and the second known as inclusion. 

 In the first the plant tissue of whatever sort from trunk to seed is 

 more or less completely permeated or replaced molecule by mole- 

 cule by silicic acid, calcium carbonate or other mineral substances 

 such as magnesium, pyrite, marcasite, limonite, etc. According 

 to the completeness of this replacement the internal structure is 

 preserved with more or less fidelity, often to such an extraordinary 

 degree that the histology is completely decipherable, and such 

 delicate objects as the mycelial threads and spores of parasitic 

 fungi or even bacteria are recognizable. Remains preserved as 

 petrifactions are relatively uncommon although characteristic of 

 regions of thermal activity like the Yellowstone Park. Calcified 



