220 PROF. J. E. MARIt OjS t THE [vol. lxXV, 



(c) Clays near the Huntingdon Road. 



I briefly referred to these accumulations in my paper in the 

 Proceedings of the Cambridge Philosophical Society, J 917, p. 68. 

 They are found on the land parallel to the Huntingdon Road on 

 the east side of the Observatory Gravel-ridge, and between it and 

 the next gravel- terrace to the east; also to some extent on the west 

 side of the Observatory ridge, on the eastern slope of the minor 

 valley. They have been exposed of recent years in shallow diggings 

 for drains and foundations only. The upper limit of these 

 accumulations is approximately 70 feet above sea-level, and the 

 lower limit apparently between -50 and 60 feet. The material 

 consists of grey clay with many rootlets (probably recent), grains 

 of sand, and small flint-pebbles and frequent derived coprolites. 

 Abundant nodules of ' race ' are distributed throughout the material 

 in most places. They vary from a quarter of an inch to nearly 

 an inch in diameter, are white, usually rather friable, and have 

 hollow centres, into which project lobe-lifce extensions of the 

 calcareous material. The greatest thickness oi the accumulation 

 that I have seen was 3 feet 6 inches in a section made when 

 the foundations of a house were being dug at/ the junction of 

 Storey's Way with the Huntingdon Road. This/deposit contained. 

 patches of sandy loam 1 to 2 yards long and aj^out 8 inches thick. 

 They occurred in elliptical lenticles arranged in a horizontal band, 

 recalling certain masses .figured by Mr. H. Dewey in a paper on 

 ■ Researches at Rickniansworth,' by him and Mr. Reginald Smith. 1 

 There are in places vertical bands of this material above the 

 elliptical patches, as though it had been introduced through 

 fissures, but it is difficult to see how cavities can have been formed 

 of so regular a character. 



In all the sections seen the clayey material seems to be roughly 

 stratified, though with sections of so shallow; a character it was 

 difficult to be certain of this. 



I may note that a similar deposit is well exposed in a pit near 

 the railway between Long Stanton and Over. This also contains 

 the ' race ' nodules, and is distinctly stratified. It is mapped by 

 the Geological Surveyors as Boulder Clay. 



Unfortunately the relationship of this accumulation to gravels 

 at higher and lower levels has not been established. In 1916 a 

 drain was cut in the field on the side of the road opposite Girton 

 College. This drain was for some distance cut through the 

 Observatory Gravels. About 200 yards south-west of the road, 

 and at a height of about 70 feet above sea-level, the drain passed 

 into a sandy yellow to grey loam, penetrated by rootlets, but 

 containing no ' race.' It resembles the sandy patches seen in the 

 clay elsewhere. The ground had been previously disturbed at the 

 junction between the gravel and the loam, so that the junction 

 was obscure. Below the loam was a sand-bed which may belong 



1 ' Archjeologia ' vol. lxvi (1915) p. 218. See Bed 2 in fig. 10. 



