O F F O S S I L S. 127 



Or THE CLASSES OF FOSSILS. 



$ XLV. Enumeration of tbe Claflcs. 



AVICEKKA, an Arabian phyfician of the e- 

 levcnth century, divided foilils into tlie four 

 dalles, of falts, earths, metals, and phiogiflic 

 bodies. In this divilion, all fubftances agreeing 

 either in external or internal character, are pro- 

 perly enough combined; and, as hitherto no 

 general arrangement has been propofcd prefe- 

 rable to this, it is no doubt worthy of being 

 continued. 



$ XL vi. Order. 



THE order of the clafies may in a great mca- 

 lure be treated as a matter of indifference; how- 

 ever, I think it right to begin with Salts, as be- 

 ing the only fubilanccs fulublc in water, and 

 which ought to be thoroughly undcrftood, in 

 order to developc the nature of the other clafies; 

 and perhaps, bccaufc they are radically united 

 with each of them, though the moll confidcra- 

 blc number of them have as yet in this ilatc c- 

 fcapcd difcovcry. 



Phlogiilic bodies I place the lad in order; for 

 thcfe by their prevailing principle approach nea- 

 rer than any of the other cluflcs to organifcd bo- 

 1' 2 dies, 



