368 Dr. Berger's reply to Mr. Henslow. [MAY, 



them presented itself. Mr. Webster obligingly lent me his 

 assistance in preparing the map and sections which accompany 

 my memoir,* but it is true that I did not consult him on subjects 

 which were not in his department. 



It will be readily conceived that I had not the means of ascer- 

 taining whether the southern part of the chain of mountains is 

 placed in my map of the Isle of Man two or three miles too far 

 to the east, according to the opinion of Mr. Henslow (p. 483;. 

 This fault may exist, and probably is not the only one. I 

 regarded this document merely as a geological map, without 

 absurdly pretending to dedicate it to geographical engineers.^ 

 I will only add, that, in my opinion, it is better as a topographi- 

 cal map of the mountainous part than those of my predecessors, 

 and that in publishing his own, Mr. H. has not rendered mine 

 useless, or superfluous. 



I must confess 1 was surprised on reading (p. 482), that I had 

 omitted to mention several formations of rocks, being persuaded 

 that I had inspected them all, with greater or less brevity, except 

 those which are volcanic. I was fearful that some unquestion- 

 able trace of volcanos, either extinct, or in activity, had escaped 

 me, but I was not long in recovering from this apprehension, 

 by observing that my critic, and 1 do not attach the same idea, 

 to what is called a formation of rocks, and that Mr. H. applies 

 this term to objects which are of very secondary importance.^: 



Mr. Henslow has found granite in situ in other places than 

 those which I have mentioned, and he has also traced its course 

 further in another direction than I have done. But did this 

 require for its narration more than three quarto pages ? The rock 

 called greuwacke,\ by those who adopt the principles of Werner, 

 is remarkable in this respect, that being composed of the remains 

 of ancient rocks, it expresses a formation of modern date, which 

 is supposed to have occurred by deposition, rather than by che- 



* I have publicly acknowledged my obligation to him. 



+ I had then only a simple pocket compass to make use of in going successively 

 from one mountain to another. 



\ I am of opinion that in Geognosy the term Formation may be defined to be an 

 assemblage of certain rocks or mineral matters, which appear, according to their 

 geognostic relations of position, to be contemporaneous or nearly so. I am at present 

 acquainted only with the following : 



1. Formation of Primitive Rocks. - 



2. Transition Rocks. 



3. Secondary Rocks (Floetz). 



4. - i — Alluvial Rocks, or matter. 



5. Volcanos. 



I leave it to those who are more capable than I am, to determine whether what is 

 called the fresh-water limestone should be added to the most recent members of the 

 third formation, or whether it is actually a distinct formation between the third and 

 fourth. 



§ Professor Jameson, by translating the first part of the German name into Eng- 

 lish, has rendered the pronunciation less harsh. 



