OF FOSSILS. 



xxx. Examination ly tbe Magnet. 



IRON, unlefs it is dcphlogifticated below a 

 certain point, is ever obedient to the magnet; 

 but this mark is particular. Various phenome- 

 na likcwife authorife a fufpicion tluit many o- 

 ther iubftanccs arc attracted by it ; therefore no 

 reliance can be had upon this as a diilinguifhing 

 character. 



xxxi. Real Utility of external and pbjfical 

 Marks. 



ALTHOUGH fuperficial criteria contribute no- 

 thing to the true knowledge of foffils, and that 

 the obfcrvation of Juvenal, fronti nutiajidtt,TNHy 

 bo well applied to them, cvcnthoughthc phy- 

 fical properties be at the fame time underllood, 

 (} xxviii. xxx.) yet we arc not altogether to pafs 

 them over in contempt. By Tuch accurate de- 

 terminations as the celebrated Werner fo fuc- 

 cefsfully attempted, they are rendered very pro* 

 per for diflinguifliing varieties ; and when the 

 eye is once habituated to them, they often lead 

 it direclly to diacritic experiments. Perhaps the 

 compofuion being thoroughly afcertained by a. 

 nalyfis, an exact comparifon may allift confi- 

 dcrably in drawing a juft inference. 



xxxu, 



