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 about 20 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.

4. Summit of field, trench 45 inches deep (40)

5. Close to summit of field, trench 36 inches deep (26)

6. Close to summit of field, trench 28 inches deep (28)

7. Near summit of field, trench 36 inches deep (24)

8. Near summit of field, trench at one end 39 inches deep; the mould here graduated into the underlying undisturbed sand, and its thickness (24 inches) is somewhat arbitrary. At the other end of the trench, a causeway was encountered at a depth of only 7 inches, and the mould was here only 7 inches thick (24)

9. Trench close to the last, 28 inches in depth (24)

10. Lower part of same field, trench 30 inches deep (15)

11. Lower part of same field, trench 31 inches deep (17)

12. Lower part of same field, trench 36 inches deep, at which depth undisturbed sand was reached (28)

13. In another part of same field, trench 9.5 inches deep stopped by concrete (9.5)

14. In another part of same field, trench 9 inches deep, stopped by concrete (9)

15. In another part of the same field, trench 24 inches deep, when sand was reached (16)

16. In another part of same field, trench 30 inches deep, when stones were reached; at one end of the trench mould 12 inches, at the other end 14 inches thick (13)

Small field between "Old Works" and "Shop Leasows," I believe nearly as high as the upper part of the latter field.

17. Trench 26 inches deep (24)

18. Trench 10 inches deep, and then came upon a causeway (10)

19. Trench 34 inches deep (30)

20. Trench 31 inches deep (31)

Field on the western side of the space enclosed within the old walls.

21. Trench 28 inches deep, when undisturbed sand was reached (16)

22. Trench 29 inches deep, when undisturbed sand was reached (15)

23. Trench 14 inches deep, and then came upon a building (14)

Dr. Johnson distinguished as mould the earth which differed, more or less abruptly, in its dark colour and in its texture from the underlying sand or rubble. In the specimens sent to me, the mould resembled that which lies immediately beneath the turf in old pasture-land, excepting that it often contained small stones, too large to have passed through the bodies of worms.

The Formation of Vegetable Mould Through the Action of Worms Page 47

19th Century English Literature

Charles Darwin

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