42 Elements of Mineralogy. 



fprinkled with water. Ferrer Italy, 117, 

 They are often formed of volcanic afhes, in- 

 durated by water, and evidently contain fome 

 proportion of iron ; the two firft are ufed as 

 lime ftones. The pietra colomblna y and tur- 

 china, are faid to be of this fort. 



Analogous to thefe is the margodes, a blu- 

 ifh grey ftone, entirely refembling clay in its 

 outward appearance, but fo hard as to cut 

 fpars, or even zeolytes, but not to fuch a 

 degree as to give fire with fteel ; dull in its 

 fracture, its texture thick laminse, and of a 

 conchoidal form; its fpecific gravity 3,877; 

 it effervefces with acids. I found it to con- 

 tain 50 per cent, of calcareous Earth, about 

 32 of argill, i of filex, and 2 of iron. 



Mr. Bergman^ in his remarks on the 

 mountains of Weft Gothland, Memoirs of 

 Stockholm, 1768, mentions a fort of rtd mar- 

 ble found near Roloock, which contains fo 

 much clay that it hardens in fire, and eveu 

 jnelts in a ftrong heat, 



SPECIES VII. 



Mild Calcareous Earth mixed with a notable 

 Proportion of Ponderous? Earth. 



Barytical Limejlone, or Marl. 



This is faid to be found both in a ftony 

 and loofe form in Derby/hire ; the former is 



faid 



