460 REPORT— 1902. 



doubt of the whole of these varieties having been in use in one and the 

 same district at the same time, the forms being to some extent adapted to 

 the flake of flint from which the arrow-heads were made, and to some 

 extent to the purposes which the arrows were to serve.' • 



The two Arbor Low specimens were probably not used many years 

 apart, for the fosse would, throughout its lower portions, and indeed 

 within 30 to 60 cm. of the present surface of the silting, fill up somewhat 

 rapidly, particularly at the bottom, owing to the fact of the sides of the 

 ditch being exposed to the erosive force of the atmosphere, the action of 

 rain and frost, and the consequent disintegration of the sides. In this 

 way it will be readily understood that the width of the Arbor Low fosse, 

 and indeed of all such ditches, at the top has increased during the process 

 of silting up and denudation of tiie sides, whilst the width of the ditch at 

 the bottom would remain very much the same as at the time of original 

 construction. Naturally the sides of some ditches would disintegrate 

 much quicker than others, the havoc played by frost and rain would leave 

 its mark much more quickly in the case of the chalk than in that of the 

 limestone, and thus the talus formed at the bottom of the ditch would be 

 deposited much more rapidly in the former than in the latter case. The 

 talus, as viewed by a spectator looking down into the ditch, would have 

 a very pronounced concave surface, so that when the sides of the ditch 

 become covered up nearly to the top, the depth of the talus in the middle 

 of the ditch would not necessarily be more than, say, 60 cm. deep in the 

 case of a fosse of the size of that at Arbor Low. After the whole 

 of the sides became completely sheltered in this way, the filling up to the 

 present surface of the central parts of the ditch from natural causes would 

 be the accumulation of centuries of finer material and stone washed in 

 and blown in from the surrounding country. Until grass began to form 

 on the vallum a more or less large proportion of the silting would be 

 derived from the slipping and washing down of material from the higher 

 ground. Finally, when the grass had begun to grow in the fosse, the 

 silting would almost cease and the surface mould would gradually increase 

 in thickness as vegetable matter decayed. This mould would probably 

 form in an increasing ratio owing to the greater luxuriance of the grass 

 caused by the greater depth of mould and the greater moisture in the 

 centre of the ditch. It appears certain that these ancient ditches, as 

 I have endeavoured to show, must have silted up (excepting the surface 

 mould of course) in a constantly and greatly diminishing ratio. 



Now the relative depths of these two Arbor Low arrow-heads does not 

 appear to difier very remarkably when the formation of the talus is taken 

 into consideration. The barbed arrow-head being on the bottom of the 

 .ditch and near the middle would become covered almost immediately the 

 •fosse was allowed to .silt up. The other arrow-head being found within 

 3 to 5 cm. of the side of the ditch at a depth of 91 cm., it will be seen 

 that it would be deposited on the talus and become covered very soon 

 after the barbed arrow-head. On the other hand, the broken lozenge- 

 shaped arrow-head was picked up out of the silting so very near the actual 

 wall of the fosse that it is just possible it may have rested on a small 

 ledge of the limestone rock, being removed therefrom by the pickaxe oa 

 the day of discovery. In any case it may be safely asserted that these 



• Ancient Stone Implements of Great Britain, 1872, p. aSO. 



