





• 







N 





*l 











ed, 



ok 



. s 



n 



ectur- 





mil 

 ant 



rfc 



:r 



jiyefr 





it* 



t 







Ch. XVIL] 



SPHEROIDAL TRAVERTIN. 



403 



crystals of sulphate of lime. After being" thus freed from its 

 rosser parts, it is conveyed by a tube to the summit of a 



a space of ten or 





chamber 



twelve feet. The current is broken in its descent by nume- 

 rous crossed sticks, by which the spray is dispersed around 

 upon certain moulds, which are rubbed lightly over with a 



om 



solution 01 soap, ana a deposition ot solid matter like marble 

 is the result, yielding a beautiful cast of the figures formed 

 in the mould. The geologist may derive f 

 ments considerable light, in regard to the high slope of the 

 strata at which some semi-crystalline precipitations can be 

 formed ; for some of the moulds are disposed almost perpen- 

 dicularly, yet the deposition is nearly equal in all parts. 



A hard stratum of stone, about a foot in thickness, is ob- 

 tained from the waters of San Filippo in four months ; and, 

 as the springs are powerful, and almost uniform in the quan- 

 tity given out, we are at no loss to comprehend the magni- 

 tude of the mass which descends the hill, which is a mile 

 and a quarter in length and the third of a mile in breadth, 

 in some places attaining a thickness of 250 feet at least. To 

 what length it might have reached it is impossible to con- 

 jecture, as it is cut off, like the travertin of San Yignone, by 

 a small stream, where it terminates abruptly. The remain- 



mattei 



the sea. 



Spheroidal structure in travertin.— But what renders this 

 recent limestone of peculiar interest to the geologist, is the 



form 



assumes 



cascade of Tivoli, afterwards to be described. (See fig. 29, 

 P. 408.) The lamination of some of the concentric masses' 

 is so minute that sixty may be counted in the thickness of 

 an mch, yet, notwithstanding these marks of gradual and 

 successive deposition, sections are sometimes exhibited of 



what might seem to be perfect spheres. 



with which the 



This tendency to a 



from 



calcareous matter is precipitated in nearly 

 equal quantities on all sides of any fragment of shell or wood, 



Lv7 « GqU i J °i the SUrfaCe ° Ver Which the mi »eral water 

 s, the form of the nucleus being readily transmitted 



D D 2 



