OF LOCHABER. 21 



once mentioned in the classics, particularly by Tacitus, who 

 notices the fact of Claudius's aqueduct having its origin on 

 the hills on their margin; "fontesque aquarum ah Simbrui- 

 " rats coUibus deductos, urbi intulit" (Ann. lib. xi. cap. 13.) ; 

 and the circumstance of Nero, who had a villa there, having 

 made it an occasional residence, is also established by the same 

 historian, who mentions the fact of that Emperor having been 

 alarmed by prodigies whilst in that retreat : " Nam quia dis- 

 " cumbentis Neronis apud Smbruina Stagna cui Sublaqueum 

 " nomen est, ictu dape mensaque disjecta erat" (Ann. lib. xiv. 

 cap. 22.) The remains of the baths of Nero, E, fig, 4. PI. VII. 

 and the mouth of the Claudian aqueduct, F, fig. 4, which are 

 both exactly on the line of shelf running around the face of 

 the hills on the north side of the valley, and which, happily for 

 our illustration, were both of a nature, that rendered water es- 

 sentially necessary for their several objects, sufficiently prove 

 that it must have owed its origin to the action of the waves of 

 the lake, which must have had its margin there, (as at E, fig 3., 

 where BE represents its ancient surface), otherwise it is mani- 

 fest that both those buildings would have been useless. The 

 wall of rock, (fig. 1.), as described by my friend, is just the 

 height of the shelf, and composed of what he called " the na- 

 " tive rock," or that which is every where prevalent in the 

 neighbourhood. This, we know from Brocchi's late work on 

 the Geology of the Appennines, is a peculiar sort of lime- 

 stone, of a pearl-grey, dusky-white, or smoke colour, with a 

 smooth earthy fracture, without lustre. But what forms a ve- 

 ry singular and striking physical corroboration of the histori- 

 cal fact, that the river once ran over the top of this rocky dam, 

 is, that the upper surface of it, (A, figs. 1, and 2.) is covered 

 by a formation of the travertina tufa, which calcareous incrus- 

 tation must have been deposited there by its waters, when 

 flowing from the lake at that elevation. The river, as is well 

 kno\vn, continues to deposit the same tufa every where, parti- 

 cularly 



