OF FOSSILS. 249 



nfccrtaincd by whatever ingredient aproaches 

 ncarcft in weight to the fuiecous. 



5 LXXIX. Compounded Earths arc not united me- 

 chanically only. 



Bt;r perhaps, all earthy compofitions are no- 

 thing elie than many fubtlc mechanical mix- 

 tures ? At the very firll view indeed there fecms 

 Ibine foundation for fuch an opinion; but a 

 more minute invcfligation furniihcs evidence of 

 a cloicr union conilrudcd on ether principles. 

 The earth of alum immcrfed in lime-water, 

 and entering into fo livid a combination with 

 the lime as not to be feparablebut by chemical 

 art, teaches us, that among primitive earths mu- 

 tual attraction has a real exillcnce. Betides, as 

 almoft all thcie mixtutcs generally form cry- 

 ftaline concretions, we have another proof, not 

 only of the minutencfs of their particles, but of 

 an union perfectly homogeneous. 



} LXXX. Genera cf Metals. 



IK the third clafs we arc to conftitutc as many 

 genera, as we have known diilind metals. 



LXXX i. Encreafed within a few Tears. 



AT the beginning of the prcfcnt century, 



eleven 



