SOILS OF CAMBRIDGE 



397 



that old channels ran along it and under it, throwing out 

 water in wet seasons, or where obstructions occurred ; and, 

 further, that all these natural features have been interfered 

 with by man during his 2000 years settlement upon the area. 



In the diagram (fig. 6) the relation of these various deposits 

 to one another is indicated : (a) represents the middens and 

 rubbish of the existing state of things ; (c) the rubbish carted 

 on to level up the ground ; and (6) the pits and hollows on 

 the old alluvial waste land. Now it is clear that the growth 

 of each of these extends over a very long period. The intra- 

 mural deposit of refuse (a) has become smaller as time went 

 on ; (c) also took a long time in the making, and was only 

 gradually carried outward towards the river, so that the earlier 

 part of (c) might be contemporaneous with (6 2 ) and a later part 

 of (c) with (6 3 ), and, although a sharp line everywhere divides 

 (c) from (6), this does not indicate a long interval between (c) 

 considered as a whole, and (6) considered as a whole. 



River 



Fig. 6. 



a. Laystalls of comparatively recent date. 



a 1 . Eubbish of every age which has accumulated about the houses of the 

 town. 



ft 1 , b 2 , ft 3 . Depressions and rubbish pits in surface of old alluvial waste land. 



c. Material carted on to ground to raise level above floods. 



d. Alluvial deposits along river. 



e. Gravel of Market Hill etc. (disturbed on top). 

 /. Gault. 



In the same diagram (x) represents the terrace of gravel (e) 

 or the spur over which the original town spread; (y) represents 

 the margin of the dry area; arid (z) the levelled up marsh land 

 on which the colleges were built. 



C. A. S. COW-MI. VOL. XI. 26 



