280 MINERALOGY OF THE ENVIRONS OF PARIS. 



clostoma. This latter fact, Cuvier remarks, shows the 

 plausibility of the opinion of Lamanon, and other natura- 

 lists, who maintain, that the gypsums of Montmartre, and 

 other hills in the basin of Paris, have been deposited from 

 fresh-water lakes. The occurrence of skeletons of quad- 

 rupeds particularly characterizes the upper bed of gyp- 

 snm, because remains of the same nature have not hi- 

 therto been discovered in the middle or lower beds of 

 gypsum. 



Beds of calcarious and clayey marl rest immediately 

 over the gypsum. Woodstone, or petrified wood of a 

 kind of palm tree, occurs in a white friable chalky marl ; 

 and in quarries which are worked in it, remains of fishes 

 and of shells, of the genera lymnasus, and planorbis, are 

 met with. The two latter do not differ very much from 

 those found in the marshes in France, a fact which 

 seems, in the opinion of Cuvier, to show, that this marl, 

 as well as the subjacent gypsum, have been deposited 

 from fresh water. In the numerous and thick beds of 

 clayey and calcarious marl which rest over this white 

 friable chalky marl, petrifactions are so rare, that we 

 cannot form any satisfactory opinion as to their forma- 

 tion. 



Over the beds of clayey and calcarious marl there rests 

 a bed of yellowish slaty marl, three feet three inches 

 thick. Kidneys of earthy calestine occur in the lower 

 part of it ; somewhat higher up we meet with a bed of 

 small bivalve shells, which are referred to the genus 

 Citherea, and between the uppermost layers of the marl 

 other species of citherea, with cerites spirobites, and 

 bones of fish, occur. This bed is not only remarkable 

 on account of its great extent, (it has been traced ten 

 leagues in one direction, and four leagues in another. 



