Calcareous Genus. 29 



Hence its fpecific gravity is only 2,456, and 

 it is called Hammite^ it contains ninety per 

 cent, of mild calcareous Earth, and ten per 

 cent, of argillaceous Earth fo firmly united 

 to red calx of iron, as to be difficultly foluble 

 even in aqua regia ; the proportion of iron 

 is not above one per cent, in this ftone, and 

 yet it feniibly colours it. 



Portland Stone, and Purbeck Stone belong 

 alfo to this clafs, the fpecific gravity of the 

 former is 2,533, an ^ f tne latter 2,680, 

 according to the experiments of Dr. Watfon y 

 who accordingly found that the latter afforded 

 more lime, 2 Watjoris Eflfays, 190. Portland 

 Stone is of a dull white colour, loofe open 

 porous texture, eafily cut, and contains a 

 fmall proportion of filex. Bath Stone refern- 

 bles the Portland, but its texture is more 

 granular and open; its fpecific gravity 

 2,494. 



Calcareous Flag-flane^ otherwife called cal- 

 careous fchifttiSv That found near Wtipd- 

 flock, and ufed for covering hcufes, is of a 

 yellowim white colour and moderately hard, 

 its fpecific gravity is 2,585, contains a little 

 clay and more iron than the Portland Stone, 



Marbles. 



