396 PROFESSOR HUGHES 



mately parallel courses. Cases where this has been observed 

 in excavations will be referred to later. On each side of 

 this recent river deposit gravel of much older date than 

 the alluvial silt rises gently into terraces which slope 

 down towards the north so that they disappear under the 

 alluvium of Midsummer Common. When the stream deserted 

 the channel which it once followed along the margin of the 

 alluvium and therefore no longer kept removing the talus 

 from the base of the steep gravel bank, that bank was soon 

 smoothed down, and is now represented by a slope so gradual 

 that almost all the features of the original terrace are oblite- 

 rated, and it is difficult to trace it. The margin of the gravel 

 on either side of the river at Cambridge is thus chamfered off 

 by the crumbling down of the river cliffs, so that the alluvium 

 overlaps the gravel, and the surface of the gravel everywhere 

 falls gently towards the river. The steep slope in the Fellows' 

 Gardens of Clare College is artificial and exceptional. 



If we could sweep all the gravel away we should find that 

 the surface of the clay which underlies it also, like that under 

 the alluvium, is grooved by old river courses also trending 

 down valley, and separated from one another by banks of 

 impervious clay, so that when the water has got into one of 

 these channels it has to follow it, and if lower down any 

 obstruction, natural or artificial, is set up, the water rises as in 

 a basin till it can find its way out over the rim. These chan- 

 nels formed a conspicuous and troublesome feature during 

 recent drainage operations along the west side of the river 

 near Newnham, and also during the recent digging for founda- 

 tions of University buildings in Downing Grounds. 



When, therefore, we are trying to explain the growth of 

 Ancient Cambridge we have to bear in mind that the early 

 settlers must have avoided such wet sites and crept along the 

 dry places furnished by the ends of the spurs and bosses of 

 gravel which sloped northward from the higher ground near 

 Barnwell and the Botanic Garden to the alluvium near St 

 John's College and Midsummer Common ; that these spurs 

 died away under the more recent alluvium on their western 

 margin also; that the base of the gravel was irregular; and 



