ITALY. LETTER XVII. 2^7 



refembling the tophaceous incruftations or fedi- 

 ments of the hot-wells at S. Quirico. It begins 

 infenfibly and thinly, as it were, to run from this 

 vein down to Marfa and towards the fea, It forms 

 different hills of a confiderable elevation, and 

 is conftantly fuperincumbent on the Gate and the 

 Galeftro. It was probably produced by the long 

 runnings and precipitations of hot boiling fulphu- 

 reous waters, which fprung from this vein, and 

 from amidft the flate and the ftratified limeftones. 

 This travertino is conftantly feen further to the 

 Weft, near monte Rot.ondo and in the Volterran. 

 Near monte Rotcndo and an ancient caftle, they 

 have found even in this calcareous tophus a vein 

 of lead and fome filvcr. The fame phenomenon 

 occurs in the Montagnwla di Siena, at Montarenti^ 

 in the quarries of the Siena- Brocatello. In this 

 place rifes from under ground a flate rock, to- 

 wards the Weft covered with many vertical dip- 

 ping beds of faline-marble, among which there is 

 that of the Erocatello d* Siena. Here the traver- 

 tino, under, the above-mentioned form, feems to v 

 iffue from between the marble and the flate ; and 

 covering the flate towards the Eaft, it dips gently, 

 flpping into and under the lower plain, which is. 

 filled with fea fand, or yellowifli arenaceous Siena- 

 tophus. 



