8 MICROSCOPICAL OBJECTS FOUND 



that nature is, on the whole, unchanged in the 

 general choice of her instruments, as well as of 

 the laws which regulate their operations ; and 

 that, consequently, if we would hope to penetrate 

 the mysterious labyrinth in which she has left 

 many of her ancient secrets concealed, we must 

 commence with the existing exhibitions of nature 

 at work, and trace backward the winding paths 

 by which she has advanced. She is still labouring 

 as of old ; and Mr. Lyell has done geologists a 

 noble service in impressing on their minds the 

 extent and power of the forces she has still at her 

 command. By thus diligently enquiring what she 

 is doing, and can do, we may arrive at a compre- 

 hension of what she has done, and of the way in 

 which it has been accomplished. 



These views apply especially to the qucestio 

 vexata of the origin of calcareous strata, many of 

 which have undergone such chemical changes 

 since they were deposited, as have rendered the 

 records of their early history obscure. An exten- 

 sive metamorphism has changed their appearance, 

 — characters, once clear and legible, are now like 

 those of a time-worn manuscript, difficult to deci- 

 pher. But in recent calcareous deposits, like that 

 of the Levant, we are able to investigate a portion 



