g'O M. D'Omalius D'Hall6y 0^ 



altogether in the liquids which deposited siliceous matter.* 

 This second marine formation thus limited, is not so concen- 

 trated as the first fresh-water formation. It begins to shew 

 itself sooner northward ; and generally forms but thin patches 

 on the right bank of the Seine ; it becomes thicker on the 

 south of that river, and constitutes those escarpments, capes, 

 and isles, which form the characteristic features of the coun- 

 try extending towards Fontainebleau, Versailles, Epernouj 

 &c.; this physical character is probably owing to the facility 

 with which water attacks this formation, the sandy mass 

 which extended from these escarpments to the patches on 

 the right bank being removed. I do not know if this sandy 

 formation has been observed more than 200 metres [636 

 feet], above the level of the sea : in other respects, it fol- 

 lows the general law of a southern dip, plunges under the 

 second fresh-water formation, and totally disappears to the 

 south of a line drawn from Chartres to Nemours. 



The second fresh-water formation, with which, from rea- 

 sons before stated, I associate the millstones without shells, 

 forms the fourth series. It covers almost the whole Paris 

 basin ; but throughout the parts where the inferior forma- 

 tions occur, it is often interrupted and not in sufiBcient force 

 to characterize the district ; advancing along the left bank 

 of the Seine it becomes thicker, and when once the line be- 

 tween Chartres and Nemours is crossed, where the sand- 

 stone without shell;- is seen to end, it forms the only remain- 

 ing Parisian formation, resting immediately on chalk, as may 

 be observed on the edges of the basin ; the deposit of fresh- 

 water limestone is so abundant in the interior as not to allow 

 any other formation to appear. This is certainly the most 

 considerable deposit of this nature that has yet been de- 

 scribed ; it is also remarkable for the solidity of the stones 

 it afiFords, the variety of siliceous matter it contains, and the 

 quantity of land and fresh-water shells discovered in it. 



* We entirely adopt this opinion of the author as to the extent of 

 tliis second marine formation. (Note of the Editor of the Annales des 

 Mines.) 



