XXXV111 



INTRODUCTION. 



.ruginous; then the argillaceous and calcareous; lastly, the 

 magnesian, barytic, Scottish, and Jargonic, in the order in 

 which they are named j the metallic substances (except iron) 

 most sparingly." After such illustrious authors, it is scarcely 

 necessary to mention the similar ideas of Lametherie*. 

 Dolomieu. In his celebrated memoir on rocks, Dolomieu observes that 

 they are chiefly composed of four principal earths, to which 

 may be joined iron, or the earth which produces it : and he 

 adds that, in this memoir, " he never considers iron under 

 the relation of its metallic properties, but as a simple earth, 

 susceptible of the same kinds of combination as the other 

 elementary earths."f In his theory, Dolomieu supposes that 

 the precipitation of the principal earths took place in the fol- 

 lowing order : the siliceous, the argillaceous, the magnesian ; 

 contemporary with which two last, was that of the ferru- 

 ginous, or, as it is here denominated from the Greek, side- 

 rous ; and last of all the calcareous J. 



In the continuation of this memoir he considers the .ag- 

 gregation of the five principal earths, estimated according to 

 its comparative force, to be in the following arrangement : 

 siliceous, argillaceous, ferruginous, calcareous, and magne- 

 sian. He remarks, as a singularity in the ferruginous earth, 

 that it often lends more hardness and solidity to masses 

 where it is simply mingled, than it can acquire when it is in 

 a state of purity. He afterwards proceeds to various observa- 

 tions on the force of adhesion of these five principal earths, 

 and gives a table to illustrate this quality. 



Patrin Patrin, who often looks upon nature with an original and 



inquisitive eye, has introduced many illustrations of the ne- 

 cessity of the siderous division. Among the primitive schisti 

 he enumerates " Ferruginous Slate. This slate is chiefly 

 composed of indurated clay, abundantly mixed with Oxyd of 

 Iron, either black or brown, but sometimes yellow or red, 



* Theorie de la Terrc, Tome i. p. 435. Tome iv. p. 45, &c. 

 f Journ. de Physique, Tome 39, for 1791, p 374. 

 I Ib. 382. 



