GEOLOGY. 285 



for one another; so that, when considering long periods and the 

 structure of the whole mass, the influence of these temporary varia- 

 tions, which arise from meteorological causes, altogether disappears, and 

 need not, therefore, be taken into account. Documents preserved in 

 the archives of Villeneuve show that, in the year 1710, the stream 

 was dammed up and its course a little altered, which makes the pres- 

 ent cone slightly irregular. That the change was not of any great 

 antiquity is also shown by the fact that, on the side where the cone 

 was protected by the dykes, the vegetable soil, where it has been 

 affected by cultivation, does not exceed two to three inches in thick- 

 ness. On this side, thus protected by the dykes, the railway cutting 

 has exposed three layers of vegetable soil, each of which must, at one 

 time, have formed the surface of the cone. They are regularly in- 

 tercalated among the gravel, and exactly parallel to one another, as 

 well as to the present surface of the cone, which itself follows a very 

 regular curve. The first of these ancient surfaces was followed, on 

 the south side of the cone, over a surface of 15,000 square feet ; it 

 had a thickness of four to six inches, and occurred at a depth of about 

 four feet (1.14 metre measured to the base of the layer) below the 

 present surface of the cone. This layer belonged to the Roman 

 period, and contained Roman tiles, and also a coin. 



The second layer was followed over a surface of 25,000 square 

 feet; it was six inches in thickness, and lay at a depth of 10 feet 

 (2.97 metres, also measured to the bottom of the layer). In it have 

 been found several fragments of unvarnished pottery, and a pair of 

 tweezers in bronze, which, to judge from the style, belonged to the 

 " Bronze " epoch. The third layer has been followed for 3,500 square 

 feet ; it was six or seven inches in thickness, and lay at a depth of 

 19 feet (5.69 metres) below the present surface; in it were found 

 some fragments of very rude pottery, some pieces of charcoal, some 

 broken bones, and a human skeleton, with a small, round, and very 

 thick skull. Fragments of charcoal were even found a foot deeper, 

 and it is also worthy of notice that no trace of tiles was found below 

 the upper layer of earth. 



Towards the centre of the cone, the three layers disappear, since, 

 at this part, the torrent has most force, and has deposited the coarsest 

 materials, even some blocks as much as three feet in diameter. The 

 farther we go from this central region the smaller are the materials 

 deposited, and the more easily might a layer of earth, formed since 

 the last great inundations, be covered over by fresh deposits. Thus, 

 at a depth of ten feet in the gravel on the south of the cone, at a part 

 where the layer of earth belonging to the " Bronze " age had already 

 disappeared, two unrolled bronze implements were discovered. They 

 had probably been retained by their weight, when the earth, which 

 once covered them, was washed away by the torrent. After disap- 

 pearing towards the centre of the cone, the three layers reappear on 

 the north side, at slightly greater depth, but with the same regularity 

 and the same relative position. The layer of the " Stone " age was 

 but slightly interrupted, while that of the " Bronze " era was easily 

 distinguishable by its peculiar character and color. 



Here, therefore, we have phenomena so regular and so well marked 

 that we may apply to them a calculation, with some little confidence 



