GEOLOGICAL AND NATURAL HISTOKY SURVEYS. 849 



9. It appears to me it can be only those who have not the task of comparison 

 Imposed on them that can complain of too much illustration. In worliing out 

 my fossils I have often regretted that you do not always give five distinct views 

 of each bivalve shell to make it understood in all its aspects. In regard to all 

 shells it is of great importance when you light upon a fertile habitat of some 

 one species to give the gradations of form that constitute varieties, often show- 

 ing such diversities in the extremes as without the gradations might be taken 

 for different species. It is important also to give the gradations from young 

 to old. 



10. On a very recent occasion I had an opportunity of examining the collec- 

 tion made by you for the purpose of enabling you to bring out in the best man- 

 ner the paleontology of New York. In my opinion it is a most valuable and 

 magnificent one. 



To the remaining questions I shall endeavor to reply on a future occasion. 

 I am, dear sir. 



Very truly, yours, 



(Signed) W. E. Logan. 



Geological Survey Office, 



Montreal, March 20, 1855. 

 To Prof. Js. Hall, 



Paleontologist of Neiv York. 



Dear Sir: In addition to the replies I sent you yesterday I have further to 

 state in answer to your questions 11, 12, 13, 14, and 15. that it must unavoidably 

 require a very considerable time to make such a collection of material as you 

 exhibited to me at Albany. Either through personal observation or the work of 

 persons in whose skill and fidelity you can place implicit reliance, it is necessary 

 to ascertain the exact locality of every specimen, iiiit merely geographically 

 but geologically, and to know how each individual bed of rock from which a 

 fossil is derived is related to all the rest. Where individual species are largely 

 developed it is requisite to ascertain what conditions in the deposit accompany 

 so fruitful a habitat, and a very large number of individuals from such a 

 locality .should be taken in order to determine what is normal and what ab- 

 normal in the form. The variations of the same species in different localities 

 must be attended to and the differences in the deposits which accompany these 

 rariations. When exposures of great thickness in any formation are met with, 

 each bed should be observed separately, and all the fossils from it should be 

 kept and registered separately until a proper comparison of the contents of the 

 bed is made with those of all the rest, and all the evidence made available 

 for a history of the accumulation of the deposits and of the events affecting the 

 life of the period. When apparent defalcations occur in the sequence especial 

 care must be exercised to ascertain whether formations supposed to be absent 

 may not be represented by some thin layer characterized by its fossils. iMuch 

 confusion and dis[)ute has occasionally arisen from the fo.ss'ls of a bed of this 

 flescription having been mingled with those of the deposits above or below. 

 To make such a collection as you have, and to attend in so doing to all such 

 details as are here enumerated. oAer a great area, more time, labor and expense 

 ivould be required than were absorbed in the original geological exploration of 

 Now York. 



It appears to me that four years is a very moderate time for the production 

 of such an original and valuable volume as each of yours on the paleontology 

 of New York and $2,500 a wholly inadequate remuneration for the work 



