by periodic vegetable growths during the gradual silting up of the ditch after the abandonment of the fort.
In the circumstances expert opinion was obviously desirable. The material was accordingly submitted to Mr. Francis J. Lewis) of the University of Liverpool, and to Mr. Robert Campbell, B.Sc., of the Geological Department of the University of Edinburgh. The results of their examination were unfortunately indecisive. Mr. Lewis came to the conclusion that there was no evidence that the alternations of clay and peat represented annual growths. The regularity and the thickness of the clay between the bands of peat, as well as the frequent occurrence of fragments of pottery, seemed to be against that theory. It looked as if the peaty matter had not been formed in situ. On the other hand, the black lines did not. appear to represent strata of turf used in filling up the ditch, since they were proved to consist of peaty wash and mosses. The silt was probably rather the sort of deposit which might be found in a ditch flooded by a strong rush of water, at certain intervals, by artificial agencies. If this view be right, there is no alternative but to suppose that the silt and peaty bands were laid down during the actual occupation of the fort. Mr. Campbell, who was fortunately able to examine the deposit on the spot, agreed that the peaty beds had not grown in situ. At the same time a careful scrutiny of the material seemed, in his opinion, to negative the idea of sedimentation by stream action, and he was inclined to consider that the ditch must have been filled up by artificial means.
The curious stratification of the west front had no parallel in that portion of the ditch excavated on the east. For the most part, the same is true as regards the south. This was doubtless due to the fact that, owing to the higher level of these ditches, the water from them would gravitate towards the west, which formed the lowest point of the system. Nor was there in the upper part, where it had been filled by the overlying clay of the later rampart, any sign of the growth of hazel and whin along the sides after the abandonment, such as was noted at Bar Hill. The evidence from the ditch, so far as obtainable, thus favours the opinion which subsequent discoveries of pottery suggested, namely, that the abandonment of the early fort was immediately, or at no long interval, followed by the construction of the later one.
The Evolution of Roman Forts
In Germany, along the Roman frontier line or Limes that ran from the Rhine to the Danube, there are many forts in which excavation has revealed
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