590 THE WONDERS OF GEOLOGY. Lect. VI. 



To enable the unscientific reader to comprehend the origin 

 and formation of these ancient fossiliferous rocks, I there- 

 fore purpose devoting the present Lecture to a general view 

 of the natural history of some of the recent animals of this 

 class, and a brief notice of the most characteristic fossil 

 species. 



2. Organic and inorganic bodies. — The beautiful 

 world in which we are placed is every where full of objects 

 presenting innumerable varieties of form and structure, of 

 action and position ; some of them being inanimate or inor- 

 ganic, and others possessing organization or vitality. The 

 organic kingdom of nature, in like manner, is separated into 

 two grand divisions, the animal and the vegetable. The 

 differences between organic and inorganic bodies are nume- 

 rous and manifest ; but it will suffice for my present purpose 

 to mention a few obvious and familiar characters. All the 

 parts of an inorganic body enjoy an independent existence; 

 if I break off a crystal from this mass of calcareous spar, 

 the specimen does not lose any of its properties, it is still a 

 group of crystals as before ; but if a branch be separated 

 from a tree, or a limb from an animal, each is rendered 

 imperfect, and the parts removed suffer decomposition, — 

 the branch withers, and the limb undergoes putrefaction. 

 If crystals, which may be considered the most perfect models 

 of inorganic substances, be formed, they will remain un- 

 changed, unless acted upon by some external force of a 

 chemical or mechanical nature ; within, every particle is 

 at rest, nor do they possess the power to alter, increase, or 

 diminish : they can augment by external additions only, and 

 decrease but by the removal of portions of their mass.* 



* These remarks must be taken in a general sense only, since recent 

 experiments have demonstrated that the molecules of inorganic matter 

 undergo modification by the slightest action of light, and variation of 

 temperature. 



" Prismatic crystals of zinc are changed in a few seconds into octa- 

 hedrons by the heat of the sun. We are led from the mobility of 



