TO 



SIR RODERICK IMPEY MURCHISON, K.C.B., G.C.St.8., D.C.L., LL.D., 



M.A., P.R.S., P.L.S., P.G.S., PRES. R.G.S., etc. 



DIRECTOR-GENERAL OF THE GEOLOGICAL SURVEY OF THE UNITED KINGDOM ; A TRUSTEE OF THE BRITISH 

 AND HUNTERIAN MUSEUMS, OF THE BRITISH ASSOCIATION FOR THE ADVANCEMENT 



OF SCIENCE, ETC., ETC. 



My dear Sir Roderick, 



In 1849, I undertook to prepare for the Palseontographical Society a series of 

 Monographs to correspond with the seven great divisions in geology. I had then but a very 

 imperfect idea of the magnitude and difficulty of the undertaking. It was at that time 

 believed that the proposed work would occupy one volume, and that it might be completed 

 in the course of four or five years ; but I soon found that to attain even an approximate 

 knowledge of the numerous species, and of the correct determination of their localities, it 

 would require geological as well as palaeontological researches to be made over nearly the 

 whole extent of the British Islands. This portion of the undertaking would have proved 

 an insurmountable difficulty but for the valuable assistance afforded me by the publication of 

 your admirable ' Silurian System/ and its follower, ' Siluria.' Through the means of which, 

 assisted by the works of other eminent geologists, I have been enabled to determine their 

 proper positions in the respective formations of the numerous species with which I have become 

 acquainted in the course of my researches. To whom, therefore, can I dedicate with greater 

 propriety the second and third volumes of my work, containing the Silurian, Devonian, Car- 

 boniferous and Permian species, than to you who have so ably and completely extricated the 

 Palaeozoic rocks and fossils from the confusion in which they were involved, previous to the 

 publication of your luminous and valuable works on those departments of geology. 



I have the honour to remain, 



My dear Sir Roderick, 

 With sincere respect and gratitude, 



Yours most faithfully, 



THOMAS DAVIDSON. 



