XXVlll PROCEEDINGS, 



form the source of the Thame. lu the valley in which Aldbury 

 is situated a stream sometimes flows, but it is soon lost in 

 swallow-holes. This was not always the case, for it was once 

 the source of the Bulbourne, which does not now rise any higher 

 up its valley than Cow-roast ; it is gradually shrinking not only 

 in length but also in volume, as is its tributary the Grade. On 

 the other hand, the northerly-flowing streams have been cutting 

 their way back into the Chalk escarpment for so long that they 

 have caused the escarpment to recede for many miles, for the 

 present Chiltern Hills are but the south-eastern slopes of 

 a much higher range which by subaerial erosion has gradually 

 been reduced in height and extent. 



The party here unexpectedly encountered a brood of plover 

 chicks running about on the grass, and some allowed themselves 

 to be taken up and fondled, but were soon released. 



Passing again thi'ough the woods, the village of Aldbury was 

 reached by a walk thence through the fields, and tea was had 

 at the " G-reyhound." A vote of thanks having then, on the 

 proposition of the President of the Society, Dr. Morison, been 

 accorded to the Director of the meeting, Moneybury Hill on 

 the opposite side of the valley was ascended, and, after further 

 geological i-emarks had been made, some of the party walked 

 back to Tring Station, while the rest cycled to their respective 

 destinations. 



The weather was very pleasant, the warm rays of the sun 

 being tempered by a cool breeze, while the delicate tints of the 

 new foliage gave a charming freshness to the landscape. 



Field Meeting, 26th May, 1906. 

 AYOT GEEEN AND HATFIELD. 



This was a joint meeting with the Geologists' Association, 

 Mr. Horace Monckton and Mr. Hopkinson being Directors for 

 the London society and the latter also for the County society. 



Assembling at Ayot Station, the brickfields near were first 

 visited. Several pits are now open, showing a few good sections, 

 which were examined in descending order, or from newer to 

 older deposits, the newer being to the east. At the highest 

 part is a little boulder-clay, not now well exposed, and below 

 that a bed of gravel referred by Prestwich to the Westleton 

 Shingle. These sviperficial deposits are only seen near the high 

 road (Hatfield to Welwyn), at the eastern end of the brickfields. 

 Below them is a little of the lower part of the London Clay 

 with its basement-bed, seen in the eastern and central pits. And 

 below again are the Reading Beds, here consisting chiefly of 

 light-coloured sand with pale-grey clay, seen in the central and 

 western pits. The Chalk, on Avhich these beds rest, is not here 

 exposed, but it may be seen in a shallow roadside cutting 

 within half a mile to the south-east, where its junction with the 



