THE GEOLOGIST 



JANUARY, 1859. 



ON THE NEOCOMIAN AND THE WEALDEN ROCKS IN 

 THE JURA AND IN ENGLAND. 



Bj M. Jules Marcou, Professor of Geology in the Federal Polytechnic 



School, Zurich. 



In June, 1827, Dr. W. H. Fitton read before the Geological Society of 

 London the following statement : — " It is obvious that, during a 

 period of time sufficient for the accumulation of the Wealden, the 

 deposition of matter in the adjacent seas could not have been 

 inconsiderable ; so that we might expect to find, interposed between 

 the strata which then formed the bottom of the sea and the Lower 

 Greensand, a series of beds coeval with the Wealden in point of date, 

 but differing from it in possessing the characters of a marine deposit, 

 and including marine shells and other productions of salt water ; with 

 which, near the shore, the productions of the land, or even the fresh- 

 water shells of the rivers, might be occasionally intermixed 



1st. That the AVealden and its marine equivalent could not both be 

 found in the same place ; and consequently (since we have the former 

 in England) that the marine beds of that date are not to be expected 

 generally in this country ; 2dly. That the marine fossils of the beds 

 cotemporaneous with the Wealden would probably be distinct, both 

 from those of the Portland group beneath, and of the Greensands 

 above them ; a consideration which gives peculiar interest to the 

 fossils of this intermediate group." Since that day, the Neocomian 



* See Observations on some of the Strata hetween the Chalh and Oocford Oolite 

 in the South of England. Transact. Geol. Soc. 2 Ser, vol. iv. p. 329. 



VOL. II. B 



