CHAP. IV. OP ANCIENT BUILDINGS. 229 



ally so deep. The mortar employed in the 

 buildings must have been excellent, for it 

 is still in parts extremely hard. Wher- 

 ever walls of any height have been exposed 

 to view, they are, as Dr. Johnson believes, 

 still perpendicular. The walls with such 

 deep foundations cannot have been under- 

 mined by worms, and therefore cannot have 

 subsided, as appears to have occurred at 

 Abinger and Silchester. Hence it is very 

 difficult to account for their being now com- 

 pletely covered with earth; but how much 

 of this covering consists of vegetable mould 

 and how much of rubble I do not know. 

 The market-place, with the foundations at a 

 depth of 14 feet, was covered up, as Dr. 

 Johnson believes, by between 6 and 24 inches 

 of earth. The tops of the broken-down walls 

 of a caldarium or bath, 9 feet in depth, were 

 likewise covered up with nearly 2 feet of 

 earth. The summit of an arch, leading into 

 an ash-pit 7 feet in depth, was covered up 

 with not more than 8 inches of earth. When- 

 ever a building which has not subsided is 

 covered with earth, we must suppose, either 

 that the upper layers of stone have been at 



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