Volcanoes of Central Asia. 159 



systems of contemporary mountains, that, in the interior of Asia 

 likewise, the four grand chains which run from east, to west are 

 of a totally different origin from the chains which lie in a direc- 

 tion north and south, or N. 30° W., and S. 30° E. The chain 

 of the Ural, the Bolor, or Beloor-tag, the Ghauts of Malabar, 

 and the Kingkhan, are probably more modern than the chains 

 of the Himalaya and the Teen-shan. The systems of different 

 epochs are not always separated from each other by consider- 

 able spaces, as in Germany, and in the greater part of the new 

 continent. Frequently, chains of mountains, or axes of uprais- 

 ing, of dissimilar directions, and belonging to epochs totally 

 different, are nearly approximated by nature ; resembling so far 

 the characters on a monument which, crossing different ways, 

 were engraved at different periods, and carry intrinsic marks of 

 their own date. Thus, in the south of France, are seen chains 

 and undulated swellings, some of which are parallel to the Pyre- 

 nees and others to the western Alps. The same diversity of 

 geological phenomena is apparent in the high land of Central 

 Asia, where isolated portions appear as it were surrounded and 

 enclosed by subdivisions, in parallel lines, of the systems of 

 mountain. 



Critical Observations wi the Ideas ofM. Alexander Brongniart^ 

 relating to the Classijication and probable Origin of Ter- 

 tiary Deposits. By A. Boue', M. D. Communicated by 

 the Author. 



Xhe " Tableau des Terrains" of M. Brongniart is well known, 

 and has been gratefully received by the scientific world. Far 

 from being disposed to remain stationary in his ideas, this found- 

 er of the true doctrine of tertiary deposits has recognised the 

 advances made in our knowledge of these formations, and has, 

 consequently, modified some of his theoretical deductions, and 

 even some of his former classifications. We are now to inquire 

 if he has carried his modifications sufficiently far, to what ex- 

 tent his new doctrines can be admitted ; and if he is always, in 

 his reasoning, in harmony with his principles. 



