CHAP. V. AND DENUDATION. 257 



moment that they had almost all undergone 

 much attrition. I speak thus after haying- 

 examined small water-worn pebbles, formed 

 from Roman bricks, which M. Henri de 

 Saussure had the kindness to send me, and 

 which he had extracted from sand and gravel 

 beds, deposited on the shores of the Lake of 

 Geneva, at a former period when the water 

 stood at about two metres above its present 

 level. The smallest of these water-worn 

 pebbles of brick from Geneva resembled 

 closely many of those extracted from the 

 gizzards of worms, but the larger ones were 

 somewhat smoother. 



Four castings found on the recently un- 

 covered, tesselated floor of the great room in 

 the Roman villa at Brading, contained many 

 particles of tile or brick, of mortar, and of 

 hard white cement ; and the majority of these 

 appeared plainly worn. The particles of 

 mortar, however, seemed to have suffered 

 more corrosion than attrition, for grains .of 

 silex often projected from their surfaces. 

 Castings from within the nave of Beaulieu 

 Abbey, which was destroyed by Henry VIII.,. 

 were collected from a level expanse of turf,, 



