CORRESPONDENCE WITH SCIENTIFIC MEN. 57 



with Greek heads and French tails, are absurdly intro- 

 duced, as they assume the truth of a theory that cannot be 

 proved, that the age of tertiary strata can be determined 

 by the proportions of recent and extinct shells. During 

 the inundations and changes which took place in the epoch 

 of the tertiary strata, the fossil remains of distant parts 

 were much intermixed. Indeed, all the little differences of 

 form, which make cabinet geologists believe shells belong 

 to different species, are often exceeded in the present day 

 by removing the animal into a new situation. 



FROM MR. BAKEWELL. 



HAMPSTEAD, (near London), February, 1838. 



M-&DEAR SIR, Having for the last three months been 

 engaged in the publication of the fifth edition of my " Geol- 

 ogy," I have scarcely written to any of my friends, except 

 through the medium of my good secretary, Mrs. B. The 

 mechanical labor of writing is a greater fatigue than 

 formerly, and I find that one subject, when I enter heartily 

 into it, is like Aaron's serpent, it swallows all the rest ; but 

 this is a constitutional habit of mind. I have long been 

 desirous of writing to you to thank you, first, for a very 

 kind letter I received from you long since, and for your 

 kind attentions to Mr. Wood, who appears to have received 

 more gratification from his introduction to you than from 

 almost any introduction in the United States. My fifth 

 edition is about two thirds through the press. I am sorry 

 to say that it will be larger than the fourth, considerably, 

 by about eighty pages. There is one new chapter on a sub- 

 ject which has hitherto been neglected by all geologists, 

 myself among the rest, although it has been admitted to 

 be one of the most extraordinary phenomena that geology 

 presents. I have not told any of my friends here what it is, 

 there is such sharp work in catching up and appropriating 

 any new observations or discoveries ; but I will inform you 



