of Science<; of (he Insl'ilute of France. 3.3^ 



The composition of thii species of the stone, from its great ana- 

 logy to that of glass, miglit be supposed to be of volcanic origin; 

 if it were not accompanied with a multitude of other kind^ which 

 have nothing in common with glass; and if the sodalites of 

 Greenland were not found in places where there is no trace of 

 subterranean fires. 



The object of geology, in the scientific form which it has at- 

 tained in modern times, is not so much to imagine, as formerly^ 

 systems upon the states through which the g]ol)e has passed, as 

 to describe exactly its existing state, and the relative position of 

 the masses which compose its exterior. 



In this last respect these masses have, it is well knoxni, been 

 distinguished into primitive, — that is, masses in which there are 

 no traces of organized bodies, and which are supposed anterior 

 to life, — and into secondary, which are all more or less filled with 

 organic remains, and which must of course have been formed 

 since these existed. These masses are besides generally different 

 both in point of form and of the materials of which they are 

 composed. It has been even for a long time believed that these 

 materials are placed in a succession of order equally determined; 

 so that no such masses as were deposited before the existence of 

 organic bodies can have been deposited since, and vice versa. 



More correct obsetvations have since shown this idea, as to 

 the depositation of the strata of the earth, to he quite erroneous* 

 It has been observed, that between these two sorts of masses 

 there exist mixtures where the ancient or primitive strata have 

 been reproduced after new or secondary formations ; that is to savj 

 «ome organized bodies which are covered by masses of the same 

 nature as those which were supposed to have ceased depositing 

 themselves since life appeared on the globe. These memorials 

 of a change from one state of things to another have been called 

 transition earths. 



It is not, however, always easy to recognise them ?;s sucli ; and 

 M. Brochant, in a memoir which he recently published, had need 

 of all his sagacity to attach to this intermediate class the greater 

 part of the valley of Tarentaise ; in as much as he had not then 

 discovered some shells, the existence of which in these rocks, as 

 since ascertained, has confirmed in a most flattering manner the 

 conjectures and the reasonings of that learned geologist. 



M. Brochant has since extended his researches on the same 

 subject, and directed tliem chiefly this year to the ancient gvf)- 

 sums which are found in such abundance in certain parts of the 

 Alps, and of whose enormous masses all travellers who have 

 crossed Mont-Cenis have taken notice. After having d<\,cribod 

 with a scrupulous exactness all the circumstances of their posi- 

 tion, and having often traversed the mountains, on the shelves 



of 



