COLLEGE DITCHES IN CAMBRIDGE 413 



present purpose, we may continue to refer to as the King's 

 Ditch. 



It is probable that in Jesus College Ditch we have an 

 ancient river bed maintained as a boundary. It has the 

 winding course of a river channel, and its general trend coin- 

 cides with that of the valley; while on the common, to the 

 north of it, there is another ditch, now almost obliterated, 

 running parallel to it and probably marking another ancient 

 river course. Many of the existing boundary ditches in " the 

 Backs " represent, as I have already suggested (p. 395), old river 

 courses. These are joined to the existing river by straight 

 artificial cuts dividing the college grounds. But the deep 

 troughs I have described above (p. 401) belong to much earlier 

 conditions, when the river bed was cut down to what is now 

 below sea level, and alluvial deposits belonging to recent con- 

 ditions filled the hollows. 



The streets in the town are raised above the level of the 

 surrounding houses and gardens, but the areas within the 

 monastic and collegiate buildings were raised above the streets. 

 Examples of this may be seen near the Colleges of Jesus and 

 Sidney Sussex, where we have the best opportunity of studying 

 the original topographical features. 



In Sidney Sussex College, which, by the courtesy of the 

 Master, I had recently a good opportunity of examining, the 

 ground within the College is raised about 3 feet above Jesus 

 Lane and Bridge Street, and the excavations for the new 

 buildings showed made ground and disturbed gravel to a depth 

 of from 9 to 11 feet. 



The grounds of Jesus College are raised well above the 

 alluvium, and the made ground encroaches over it, while the 

 street face is kept up to the raised level of Jesus Lane which 

 is on the gravel. The nunnery of St Rhadegund was built 

 on lower ground, as seen by the depth of the base of the 

 recently discovered arches of the Chapter House, below the 

 level of the existing cloisters. But when we examine the 

 adjoining streets, we find that they are raised above the level 

 of the dwelling-houses and gardens. On the north side of 

 King Street, where excavations show gravel on gault, the 



C.A.S. Comm. VOL. XI. 27 



