236 FORMATION AND GROWTH OF 



Romans 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 thickness of five 

 sheets of foolscap paper, or, to put it differently, 

 one inch growth in every 35*4 years. Further- 

 more, all may not be due to the vegetable decay ; for 

 as the field is near Caerleon, it is probable that it 

 has often been " topdressed," a process which would 

 quickly add to the depth of the soil. It may be 

 here mentioned, that some years since, a field in 

 the north part of the County Tipperary was broken 

 up that had a soil fourteen inches deep, and this field 

 was known by a man seventy years old to be exactly 

 110 years in grass. As the average depth of soil in 

 that part of the county is from ten to twelve inches, 

 it would leave about 2 *5 inches of soil to grow in the 

 century; which is very similar to the results obtained 

 near Caerleon. 



Some soils are ready made when they are deposited 

 on the surface ; as, for instance, the particles carried 

 down by flood and deposited on callows, corcasses, 

 and other alluvial flats. Another instance is wind- 

 borne soil, clouds of fine particles being carried 

 during dry windy weather from high to low land, 

 especially if the former is in tillage. Even grass-land 

 may supply such materials as we have remarked 



