As the foundations of the walls generally lie at a considerable depth, they will either have not subsided at all through the undermining action of worms, or they will have subsided much less than the floor.This latter result would follow from worms not often working deep down beneath the foundations; but more especially from the walls not yielding when penetrated by worms, whereas the successively formed burrows in a mass of earth, equal to one of the walls in depth and thickness, would have collapsed many times since the desertion of the ruins, and would consequently have shrunk or subsided.As the walls cannot have sunk much or at all, the immediately adjoining pavement from adhering to them will have been prevented from subsiding; and thus the present curvature of the pavement is intelligible.
The circumstance which has surprised me most with respect to Silchester is that during the many centuries which have elapsed since the old buildings were deserted, the vegetable mould has not accumulated over them to a greater thickness than that here observed.In most places it is only about 9 inches in thickness, but in some places 12 or even more inches.In Fig.11, it is given as 20 inches, but this section was drawn by Mr.Joyce before his attention was particularly called to this subject.The land enclosed within the old walls is described as sloping slightly to the south; but there are parts which, according to Mr.Joyce, are nearly level, and it appears that the mould is here generally thicker than elsewhere.The surface slopes in other parts from west to east, and Mr.Joyce describes one floor as covered at the western end by rubbish and mould to a thickness of 28.5 inches, and at the eastern end by a thickness of only 11.5inches.A very slight slope suffices to cause recent castings to flow downwards during heavy rain, and thus much earth will ultimately reach the neighbouring rills and streams and be carried away.By this means, the absence of very thick beds of mould over these ancient ruins may, as I believe, be explained.Moreover most of the land here has long been ploughed, and this would greatly aid the washing away of the finer earth during rainy weather.
The nature of the beds immediately beneath the vegetable mould in some of the sections is rather perplexing.We see, for instance, in the section of an excavation in a grass meadow (Fig.14), which sloped from north to south at an angle of 30 degrees 40 seconds, that the mould on the upper side is only six inches and on the lower side nine inches in thickness.But this mould lies on a mass (25.5 inches in thickness on the upper side) "of dark brown mould," as described by Mr.Joyce, "thickly interspersed with small pebbles and bits of tiles, which present a corroded or worn appearance.The state of this dark-coloured earth is like that of a field which has long been ploughed, for the earth thus becomes intermingled with stones and fragments of all kinds which have been much exposed to the weather.If during the course of many centuries this grass meadow and the other now cultivated fields have been at times ploughed, and at other times left as pasture, the nature of the ground in the above section is rendered intelligible.For worms will continually have brought up fine earth from below, which will have been stirred up by the plough whenever the land was cultivated.But after a time a greater thickness of fine earth will thus have been accumulated than could be reached by the plough; and a bed like the 25.5-inch mass, in Fig.14, will have been formed beneath the superficial mould, which latter will have been brought to the surface within more recent times, and have been well sifted by the worms.
Wroxeter, Shropshire.--The old Roman city of Uriconium was founded in the early part of the second century, if not before this date; and it was destroyed, according to Mr.Wright, probably between the middle of the fourth and fifth century.The inhabitants were massacred, and skeletons of women were found in the hypocausts.Before the year 1859, the sole remnant of the city above ground, was a portion of a massive wall about20 ft.in height.The surrounding land undulates slightly, and has long been under cultivation.It had been noticed that the corn-crops ripened prematurely in certain narrow lines, and that the snow remained unmelted in certain places longer than in others.These appearances led, as I was informed, to extensive excavations being undertaken.The foundations of many large buildings and several streets have thus been exposed to view.The space enclosed within the old walls is an irregular oval, about 1 mile in length.Many of the stones or bricks used in the buildings must have been carried away; but the hypocausts, baths, and other underground buildings were found tolerably perfect, being filled with stones, broken tiles, rubbish and soil.The old floors of various rooms were covered with rubble.As I was anxious to know how thick the mantle of mould and rubbish was, which had so long concealed these ruins, I applied to Dr.H.Johnson, who had superintended the excavations; and he, with the greatest kindness, twice visited the place to examine it in reference to my questions, and had many trenches dug in four fields which had hitherto been undisturbed.The results of his observations are given in the following Table.He also sent me specimens of the mould, and answered, as far as he could, all my questions.
MEASUREMENTS BY DR.H.JOHNSON OF THE THICKNESS OF THE VEGETABLE MOULD OVER THE ROMAN RUINS AT WROXETER.
Trenches dug in a field called "Old Works."(Thickness of mould in inches shown in parenthesis--DP.)1.At a depth of 36 inches undisturbed sand was reached (20)2.At a depth of 33 inches concrete was reached (21)3.At a depth of 9 inches concrete was reached (9)Trenches dug in a field called "Shop Leasows;" this is the highest field within the old walls, and slopes down from a sub-central point on all sides at about an angle of 2 degrees.