730 Mr. Lonsdale on the Age of the 



the existence on the Tartar side of the Himalaya mountains of a secondary 

 formation, not by specific identifications, but by the structure of the cham- 

 bers of the shells being of that peculiar nature, which is found only in Ammo- 

 nites of the secondary series. It is not necessary to quote examples of dis- 

 tricts, nearer home, which have been identified by organic remains. I beg, 

 however, it may be clearly understood, that in advocating the value of fossils, 

 I would not expunge from the geologist's consideration the aid to be derived 

 from order of superposition, and, under a right control, from the use of mi- 

 neral composition and lithological structure. I would also advise him not to 

 depend upon his own limited sources of knowledge, but to seek the aid of the 

 philosophical zoologist, who can teach him to reason justly on the distribu- 

 tion of animal life — the accidents to which it is liable — the changes which 

 such accidents may produce, or the means provided by nature to resist them 

 — and on the effects which a permanent alteration in the inhabiting medium 

 may work on the form and size of a shell or coral. 



1 will now point out two cases, in which errors have apparently been com- 

 mitted by attempting to establish a parallelism of formations by mineral cha- 

 racters, and an insufficient inquiry into the organic remains. 



At the commencement of the present year my attention was more particu- 

 larly redirected to M. Dumont's work on part of Belgium, published in 1832*, 

 and especially to his identification of the formations contained in that district 

 with those of the Silurian System. M. Dumont divides the terrain anthraxi- 

 fere of M. d'Omalius d'Halloy, which occurs immediately beneath the true 

 coal-measures, into the following four systems : 



1. Systeme calcareux superieur. 



2. Systeme quartzo-schisteux supdrieur. 

 S. Systeme calcareux inferieur. 



4. Systeme quartzo-schisteux inferieur. 



Beneath the last occurs the teirain ardoisier. 



It was apparently no part of M. Dumont's object at that time to place the 

 Belgian systems on a parallel with the then established formations of England, 

 though the list of fossils from the Si/stkme calcareux superieur identifies it 

 completely with the mountain-limestone. M. Dumont, it is true, considers 

 his lowest systeme to be the representative of the old red sandstone ; but the 

 identification was made on mineral characters, and at the suggestion of Mr. 

 Murchison. 



The Si/stbme quartzo-schisteux superieur was placed by Dr. Buckland in 



* Memoire sur la Constitution Geologique de la Province de Liege, 1S32. 



