426 



DOMAIN XII. VOLCANIC. 



nearly the same principles as puzzolana, only the 

 calcareous seems more plentiful in this. 



" Artificial tarras, or puzzolana, is made by 

 burning clays or slates that abound in iron, and 

 then grinding them to a fine powder."* 

 of Ireland. A red substance is found in the north of Ireland, 

 particularly in Lord Antrim's Deer-park, near 

 Glenarne, which has a burnt appearance, and 

 much resembles the puzzolana of the extinct vol- 

 canoes of France. It might perhaps be applied 

 to architectural purposes. Faujas, who rendered 

 a service to his country in discovering the puzzo- 

 lanas of Vivarais, gives the following observa- 

 tions'^ 



" Puzzolanas are an object of the first utility in 

 hydraulic constructions. We cannot build with 

 solidity in the sea, without using this volcanic pro- 

 duction, by mixing it with two portions of lime to 

 one of this natural cement, of which a well- united 

 mortar is formed. Vitruvius has, in his architec- 

 ture, devoted a chapter to the origin of this sub- 

 stance, and the property it possesses of hardening 

 very soon in sea-water, as well as fresh, when it 

 has been amalgamated with strong lime ; it then 



* Kirwan, Min. i. 411. 



f Annales du Museum . It is truly surprising that he has omitted 

 this important article in his large Classification of Volcanic Sub- 

 stances. Geologic, tome ii. p. 401 678. 



Uses of 

 puzzolana. 



