DOMAIN V. CALCAREOUS. 



where the calcareous substance has assumed a 

 sparry grain, and stalactitic forms, are common 

 in travertine. Sometimes these cavities have 

 been since filled by a calcareous stalactite, 

 whiter, of a finer grain and harder. This is the 

 origin of those white spots; the regularity of 

 which, has caused them to be mistaken for ma^ 

 rine bodies enveloped in its paste. Travertine 

 contains no remains of marine substances ; but 

 sometimes it affords fragments of vegetables. 



" It is not doubted but travertine owes its 

 origin to the depositions of the Anio ; deposi- 

 tions which, in the plain, may have formed a 

 more solid and compact rock; because its cur- 

 rent was less rapid, and perhaps its waters more 

 stagnant in several places. Not far from the 

 quarry of travertine is the Solfatara, so called 

 on account of the great heat of its waters, which 

 abound in sulphuric hydrogen gas, and form a 

 considerable sediment of calcareous matter. A 

 Cardinal d'Este caused the canal to be dug; 

 which conveys the waters of the lake to the 

 Anio. The calcareous depositions are there so 

 abundant, that, if every three years it was not 

 cleaned out, it would be closed up, notwith- 

 standing its breadth and depth. The water 

 which runs in the canal, on meeting with bits of 

 rush or other bodies, covers them with a white 



