FOSSILS, AND HOW THEY ARE FORMED 13 



watched the leaves saihng to the ground to be 

 covered by mud or sand at the next rain, or 

 dropping into the water, where sooner or later 

 they sink, as we may see them at the bottom 

 of any quiet woodland spring. 



Impressions of leaves are among the early 

 examples of color-printing, for they are fre- 

 quently of a darker, or even different, tint from 

 that of the surrounding rock, this being caused 

 by the carbonization of vegetable matter or to 

 its action on iron that may have been present 

 in the soil or water. Besides complete miner- 

 alization, or petrifaction, there are numerous 

 cases of incomplete or semi-fossilization, where 

 modern objects, still retaining their phosphate 

 of hme and some animal matter even, are 

 found buried in rock. This takes place when 

 water containing carbonate of lime, silica, or 

 sometimes iron, flows over beds of sand, ce- 

 menting the grains into solid but not dense 

 rock, and at the same time penetrating and 

 uniting with it such things as chance to be bur- 

 ied. In this way was formed the " fossil man " 

 of Guadeloupe, West Indies, a skeleton of a 

 modern Carib lying in recent concretionary 



