SESSION 1899-1900. Ixxv 



tlic loss of nitrogen from the soil in drainage. From tlio absence 

 of vegetation the amount of water percolating through them is 

 greatly in excess of anytliing which occurs with soil in its natural 

 condition, and the loss of plant-food is more considerable. Their 

 results are calculated for what is called the "harvest-year" 

 (September 1 to August 31). 



In reply to a question, Mr. Willis pointed out that the pea and 

 the sainfoin ditl'er in their habits of growth, the pea being an 

 annual and the sainfoin a perennial. Leguminous plants, which 

 have to continue their existence for more than one year, possess 

 the power of storing up in the nodules, which are formed on their 

 roots, plant-food for subsequent years. It may be mentioned that 

 the sainfoin was formerly called " St. Foine." 



The meeting, which proved a most interesting one, concluded 

 with a walk through Kothamsted Park and tea at Harpenden. 



Field Meeting, 30th June, 1900. 

 EUISLIP EESERVOIR. 



The last of the field meetings of this Summer was devoted to 

 a visit to Ruislip Reservoir, for the first time in the annals of the 

 Society. Nearly all the members cycled from Watford, under the 

 dii'ection of Mr. Hopkinson, proceeding along Hamper Mill Lane, 

 by Oxhey Woods, and through Frith Wood to Northwood Station, 

 where it had been arranged to meet those who came by train. 



From Northwood a field-path was taken to the Reservoir, and 

 near its foot, just before leaving Ruislip Common, the Director 

 gave a brief summary of the geological changes which have 

 occun'ed in the district since Silurian times, tracing in succession 

 the upheaval in South Herts and North Middlesex of the Silurian 

 and Devonian rocks ; the deposition during long ages of beds of 

 which not a trace remains in this district, which may have been 

 a land-area all this time ; the deposition of the Cretaceous rocks ; 

 the origin, upheaval, and denudation of their highest member, 

 the Chalk ; and the deposition, upheaval, and denudation of the 

 Tertiaries. The advance of the great Scandinavian ice-sheet as 

 far south as the range of hills which had been crossed between 

 Watford and Northwood was then described, with its subsequent 

 retreat and the elevation of the land, again to subside to pretty 

 near its present level about the time when the Straits of Dover 

 were formed, permanently separating England from the Continent 

 of Europe. And finally, the foldings of the strata were described, 

 or rather, perhaps it should be said, the slight deflections in the 

 dip due to lateral pressure or shrinkage, which it was shown had 

 probably given rise to the lines of outliers of the Tertiaries on the 

 Chalk, and of inlicrs, showing the Reading Beds and sometimes 

 the Chalk exposed beneath the London Clay, one such inlier of the 

 Reading Beds, surrounded by the London Clay, extending from 

 Pinner to the spot on which they were now standing. 



