XXXU PEOCEEDINGS OF THE 



whicli runs roughly parallel to the Icknield "Way and to the main 

 ridge of the higher chalk beds lying several miles to the south and 

 south-east. This latter ridge constitutes the water-parting between 

 the valley of the Thames and that of the Rhee, or Cam, in which 

 Eoyston and the Heath lie. The view across the shallow valley of 

 the Ehee is bounded by a range of hills which dies away to the 

 west, and allows in that direction an extensive view over more 

 distant country. 



Looking due west the main source of the Rhee is well marked 

 by the high tower of Ashwell Church, about six miles distant, and 

 a little to the left two large elms, standing on the summit of a hill, 

 the most elevated point of a ridge transverse to the main lines of 

 hills bounding the river-basin, define the head of the valley. 

 Prom Ashwell the small and sluggish river winds through the 

 valley to join with other streams to form the Cam as it is found 

 at Cambridge. 



Although there is no surface-drainage on the south-eastern slope 

 of the valley, where the Chalk absorbs all the rain which falls on 

 it, the water percolating through this pervious stratum at length 

 encounters the more clayey and less pervious beds of the Chalk 

 Marl ; and along the outcrop of the Totternhoe Stone, lying on the 

 top of the marl, a number of small streams rise to feed the main 

 river. 



Looking back towards the south and south-east, the main line of 

 chalk hill is seen running up to a height of somewhat over 500 feet. 

 This consists of the lower part of the Upper Chalk, resting on the 

 Chalk Rock, and capped by thin beds of boulder-clay, which latter 

 give a supply of surface-water to the villages which lie along the 

 crest of the ridge and on its southern slope. Prom a little below 

 the crest of the ridge the outcrop of the Lower Chalk, given as 

 300 feet thick by the Geological Survey, forms the wide band of 

 undulating country sloping to the bottom of the valley. The beds 

 dip generally about four degrees south. The Lower Chalk lies on 

 the Totternhoe Stone, a bed of sandy chalk, quarried for building 

 near Ashwell. This in its turn rests on the Chalk Marl, which is 

 about 60 feet thick, and has at its base the remarkable bed of phos- 

 phatic nodules, resulting, as has been shown by Mr. Jukes-Browne, 

 fi'om the denudation of the upper part of the Gault — the nodules of 

 phosphate of lime scattered through that bed having been collected 

 by the removal of the clay of the bed itself into a bed of only a few 

 feet in thickness, forming the base of the Chalk Marl. Beyond 

 this the Gault is found. The range of hills forming the opposite 

 side of the valley being an outlier from the main mass of chalk cut 

 off from this main mass by the wearing out of the valley by the 

 gradual denuding action of the river, gives the same succession of 

 beds in ascending order, as high as the Lower Chalk, viz. Gault, 

 phosphatic-nodule or " coprolite " bed. Chalk Marl, Totternhoe 

 Stone, and Lower Chalk. 



Turning to the west and looking over the extensive expanse of 

 country in the valley of the I vol and Ouse, where the outlier 



