OF ORGANIC NATURE. 43 



great majority of cases, have lived and died in the very 

 spot in which we now find thera^ or at least in the 

 immediate vicinity. You must all of you be aware — 

 and I referred to the fact in last Monday's lecture — 

 that there are vast numbers of creatures living at the 

 bottom of the sea. These creatures, like all others, 

 sooner or later die^ and their shells and hard parts lie 

 at the bottom ; and then the fine mud which is being 

 constantly brought down hj rivers and the action of 

 the wear and tear of the sea, covers them over and pro- 

 tects them from any further change or alteration ; and, 

 of course, as in process of time the mud becomes har- 

 dened and solidified, the shells of these animals are 

 preserved and firmly embedded in the limestone or 

 sandstone which is being thus formed. You may see 

 in the galleries of the Museum upstairs specimens of 

 limestones in which such fossil i-emains of existing 

 animals are embedded. There arc sonae specimens in 

 which turtles' eggs have been imbedded in calcareous 

 sand, and before the sun had hatched the young turtles, 

 they became covered over with calcareous mud, and 

 thus have been preserved and fossilized. 



. Not only does this process of imbedding and fossiliza- 

 tion occur with marine and other aquatic animals and 

 plants, but it affects those laud animals and plants 

 which are drifted away to sea, or become buried in 

 boss or morasses : and the animals which have been 

 trodden down by their fellows and crushed in the 

 mud at the rivers bank, as the herd have come to 

 drink. In any of these cases, the organisms may be 

 crushed or be mutilated, before or after putrefaction, 

 in such a manner that perhaps only a part will be left 



