•[ 232 ] 
That iron has been, and is now, in a fluid date, 
percolating through the earth, and that it fubfides, 
chryftalifes, or is precipitated, to form different bodies, 
is demonflrated by the black and red bloodftone, by 
fome beautiful Aaladfites, which are almoA pure iron, 
by the eagle-ftone, by figured pyrites, by native vitriol, 
and by native crocus. 
When this fluid iron penetrates a rock of fand- 
ftone, and only dains the furface of each grain, of a 
brownifh, reddifh, or yellow colour, it becomes only 
land and crocus; but, when it is joined with the 
chryftaline matter in a fluid date, in the very adt of 
chryflalifation of each grain of fand it incorporates 
with it, its weight and hardnefs is increafed, and then 
it becomes emery. 
The earth of the mountains and hills is of the 
fame nature as that of the rock below. If it is lime- 
done, the foil cad into any acid liquor will boil up 
with a violent effervefcence, and the acid will diflolve 
it. 
If the rock below be fand-done, or plader-done, 
or emery, the earth of that hill or mountain will 
remain quiet in the acid, and there is no effervefcence 
nor diflolution. 
I have often obferved, that, when the rocks below 
ane mixed, calcary and noncalcary, the foil of the 
furface is alfo of a mixt nature; and I always found 
the a&ion of the acid to be weak or flrong upon thefe 
earths, in proportion to the fort of done with which 
they abound. 
Thirty one leagues fouth ead of Madrid, and five 
leagues fouth of the fource of the river Tagus, is 
fituated the town of Molina Aragon, capital of a 
4 lord fh ip 
