PREFACE. Vli 



by the writings and conversations of his pupils, 

 and have contributed materially to the advance- 

 ment of this branch of natural history in Ger- 

 many, France, and also in Great Britain. Pe- 

 trifactions are no longer viewed as objects of 

 mere curiosity, as things isolated and unrelated 

 to the rocks of which the crust of the earth is 

 composed ; on the contrary, they are now con- 

 sidered as one of the most important features 

 in the strata of all regions of the earth. By 

 the regularity and determinate nature of their 

 distribution, they afford characters which assist 

 us in discriminating not only single beds, but 

 also whole formations of rocks ; and in this 

 respect they are highly interesting to the geog- 

 nostical inquirer. To the geologist this beau- 

 tiful branch of natural history opens up nume- 

 rous and uncommonly curious views of nature 

 in the mineral kingdom: it shows him the 

 commencement of the formation of organic 

 beings, it points out the gradual succession in 

 the formation of animals, from the almost pri- 

 mseval coral near the primitive strata, through 

 all the wonderful variety of form and structure 



