WATFORD NATURAL HISTORY SOCIETY. XIX 



but that we do not get the lowest beds of the Tertiary series 

 immediately overlying the Chalk, thii-ty or forty feet of marine 

 sands known as the Thanet sands, not represented here, being 

 found on the opposite side of the Thames, between the Chalk and 

 the Woolwich and Reading beds, and thinning out under London. 

 Here also, he said, the AVoolwich series consists of marine beds, 

 containing marine shells, while south of London the shells are all 

 of fresh-water or estuarine species, showing that in the old 

 Tertiary times in the south there was land over which rivers 

 flowed, while there was more or less open sea to the north. Over- 

 lying the Woolwich and Reading beds the pebble beds at the 

 base of the London Clay, rounded on an old sea-shore, mark the 

 commencement of a change — a change here from temperate to 

 tropical conditions, as shown by the fauna and flora. 



Lea\'ing Watford Heath, and descending the steep slope of the 

 Tertiary escarpment, along the edge of which flows the river 

 Colne, the gravel-pits at Colney Butts were soon reached, and 

 afforded evidence of a climate — within comparatively recent times 

 — very different from that of the London Clay period ; for the 

 gravel here is of glacial origin, and pebbles of quartzite and other 

 rocks which could not have come from a nearer point than Charn- 

 wood Forest, and may have been brought by the agency of ice 

 from Cumberland or Wales, were found associated with flints from 

 the Hertfordshire Chalk, and with fi-agments of the Hertfordshire 

 conglomerate. 



Here the party dispersed, and most of those who' had come from 

 London were very kindly entertained at tea, at Watford House, 

 by Dr. Brett. 



Field Meeting, 9th June, 1875. 

 Bricket "Wood and Munden Park. 



As on the 1st of May, rain, though in heavy partial showers 

 instead of as then in a continuous general downpour, threatened to 

 put a stop to the iutended arrangements ; but fortunately it was 

 late in the afternoon when the start was to be made, and the rain 

 liad ceased when the members left Watford for Bricket Wood, 

 where it was proposed to spend most of the evening in collecting 

 plants, insects, and microscojjic objects. 



Amongst the rarer plants found in flower, Limosella aquatica, and 

 Neottia Nidus-avis (the bird's-nest orchis), may be mentioned ; and 

 several insects of considerable rarity were collected. 



Here the party separated, — some remaining in the wood to return 

 to Watford by train, and others returning on foot by Bricket Wood 

 Common, Munden Park, and Berry Wood. In crossing the Colne 

 in Munden Park, the yellow water-lily (Nupliar luteaj and the 

 yellow flag firis PseudacorusJ were seen in profusion in full 

 bloom, and in the hedges the dog- wood f Cormis sanguineaj was 

 observed to be just coming into flower. " Otterspool " was again 

 visited, by the kind permission of the proprietor, and the pool, 



