350 G. H. Kinahan — On the Growth of Soil. 



twelve acres, has a small water table on the north and south, and 

 lies in a rock basin, that bears east and west. The eastern margin of 

 this rock-basin, previous to the drift being deposited on it, was much 

 lower than the western, and even afterward all the water would 

 have flowed to the Corrib, had not the growth of the soil formed a 

 barrier. 



Mr. John Edward Lee, F.S.A., F.G.S., the translator of Dr. 

 Keller's "Lake Dwellings of Switzerland," in a note on the depth 

 of soil covering the " Mainland Settlement of Ebersberg," records 

 a remarkable growth of soil at Caerleon, South Wales. Mr, Lee 

 thus writes : "In a field which forms the south-west portion of the 

 ancient city of Isca Silurum, I have frequently excavated for the 

 sake of archaeology, and in one instance, when the summer was 

 dry, the grass showed where walls were probably to be found, indi- 

 cating the ancient Eoman houses forming the corner of the inhabited 

 portion, an open space of the street being between them and the 

 city walls. It was, however, very singular that these indications, 

 though correct, were not verified till the ground had been excavated 

 to a depth of five or six feet ; and before the actual base of the wall 

 and the floor of the street were reached, a tall labourer was entirely 

 hidden from view. The first foot or two may be accounted for by 

 the rubbish when the place was destroyed, but as no soil is likely 

 here to have been brought down by floods, we are almost obliged to 

 attribute the remaining four or five feet to the annual addition of 

 vegetable mould. The excavation above referred to, is not the only 

 fact which indicates a great accumulation of soil ; a handsome 

 tesselated pavement lately discovered in the churchyard was four or 

 five feet below the present surface, etc., etc." ^ This is a startling 

 fact in favour of the growth of soil, by vegetable decay ; and Mr. Lee 

 further states, in a subsequent communication on the subject : " The 

 old town of Isca is on a tongue of land slightly above the flats on 

 the rivers' banks (the Usk and the Avon Llwydd), and from the 

 situation there is no chance whatever of any earth being brought 

 down from the hills to the place I mentioned." Although ap- 

 parently so large in the aggregate, yet, when the yearly amount is 

 calculated, it seems not so large. It must be about 1700 years since 

 the Eomans occupied the site, and if two feet are allowed for the 

 depth of the debris of the building, there will be four feet to be 

 formed by the growth of the soil : this is equal to 2-82 inches in a 

 century, or -028 inch annual growth ; scarcely equal to the thick- 

 ness of five sheets of foolscap paper, — or, another way to explain it, 

 one inch growth in every 34-6 years. Furthermore, all may not be 

 due to the vegetable decay; for, as the field is near Caerleon, it is 



bog. "When the lake was first visited in the early summer this drain had just been 

 opened, about five feet deep, to make up the fences, and although it did not reach to 

 the bottom of the peat, yet it was lower than the western embouchure^ and carried off 

 all the summer water. At a subsequent visit, neaily two years afterwards, the 

 eastern cut was choked up by aquatic plants, among and behind which a peaty sedi- 

 ment had been deposited, and thereby formed a dam, which drove the summer water 

 to flow westward, to the Boliska. 

 ^ Keller's Lake Dwellings, p. 367 footnote. 



