EXPLANATION of PLATE I. THEORY of the EARTH. 



FIG. i. Section of an iron-ftone feptarium, cut horizontally, as 

 it lies in its bed. 



FIG. 2. Another feptarium, cut both horizontally and perpen- 

 dicularly. 



FIG. 3. Part of a feptarium, the divifions of which are more 

 in ftraight lines. 



All thefe three are of the fame dimenfions with the 

 fpecimens. 



FIG. 4. Part of Fig. 3. reprefenting the portion included within 

 a, b y c, d, e, which is magnified, in order to mow the 

 cryftallifed cavity of the fepta. 



