56 Institute of France. 



The aggregnte rocks are divided according as the cement which 

 unites them is more or less apparent, and according to the nature 

 of this cement and the grains which it a;;ghitinates. 



In this work, so important for serving as the l)afiis for the 

 History properly so called of Rocks, the author has throughout 

 preserved the names given them by M- Ilaiiv in the arrange- 

 ment which he has made of them in the Museum of Natural 

 History. 



M. iirongniart has also represented to the Class the division 

 which he thinks ought to be e>.tal)lished between rocks con- 

 sidered with respect to the date of their formation, and to the 

 remains of organized bodies which thev contain, and which are 

 the strongest marked indications of those aeras. Underneath all 

 the rest are the gi'anitic strata, without organized bodies, and 

 the most ancient with which we are acquainted : the soils which 

 cover them contain but a small quantity of organic remains, and 

 almost all are zoophytes : a third series, that of the svenitic 

 strata, yields none, as if their production had been suddenly in- 

 terrupted : in the fourth series shells begin to appear, and 

 chiefly those which are called conma Ammonis : the fifth and 

 sixth classes of strata are characterized by the grvpliites and the 

 cerites, which prevail among their shells : lastly, there are strata 

 the distribution of which is so irregular that we cannot classify' 

 them, in the order of time : these are trapp rocks on the one 

 hand, and on t!ie other those which result from tb.e ejections of 

 volcanos. With all these groups, strata of transport are mixed, 

 productions of violent motions occasioned by revolutions, and 

 •which are sufficiently correct indicators of the moment at which 

 each has commenced. 



The well known phaenomenon of the fall of the leaves in autumn 

 is still the subject of some discussions with respect to its causes, 

 and still gives rise to various observations. M. Carnot, member 

 of the section of mechanics, but whose active mind embiaces 

 every department of science, having remarked that certain trees 

 begin to throw oft' their leaves from top to bottom, anrl vice versa ; 

 M. Palissot de Eeauvois, member of the section of botanv, has 

 inquired into the cause of this dift'erence. He found that in 

 general the species in which the aut'amnal shoots consist of 

 simple prolongations of the extremities of the branches, are first 

 stripped at bottom, and that those in wl.ich this shoot takes 

 place by small lateral branches, begin to tln-ow off the leaves at 

 top ; or, m other words, that the last grown leaves are also the 

 last which fall off. Duhamel, who had made a similar remark, 

 was astonished that those leaves which ought to be most tender 

 esisted the frost longest : this proves that it is not the frost which 

 makes the leaves fall off, but that their fall is a necessary and 

 ' ' ' ■ CO- 



