Professor J. W. Gregory — The Danbury Gravels. 531 



across the middle of the area marked as boulder-clay, but without 

 finding any trace of that material. The stones on this area include 

 no Jurassic sandstones, no large unrolled flint nodules, and no chalk ; 

 and the proportions of the stones present, viz. 45 per cent subangular 

 flints, 25 per cent pebbles from the Eocene shingle beds, and 

 30 per cent of quartz and quartzites, is much the same as in the 

 adjacent redeposited Danbury gravel. The boulder-clay was perhaps 

 marked here owing to the occurrence of some patches of soil 

 which are white owing to the abundance of quartz sand and flint 

 fragments. The boulder-clay in this area is confined to lower levels 

 than the Danbury gravels. 



The evidence for the pre-Glacial age of the Danbury gravels does 

 not rest alone on the absence of material derived from the glacial beds. 

 The general physiographic evidence appears conclusive. Glacial beds, 

 including boulder-clay and glacial gravels, are widespread over the 

 Mid-Essex plain at the level of about 200 feet, and they rise gradually 

 north-westward to 300 and 400 feet; but around Chelmsford the 

 boulder-clay does not occur on the higher ground, and the Danbury 

 hills must have stood like an island above the level of the plain on 

 which the boulder-clay was deposited. The main topography of 

 Essex was pre-Glacial. The banks of the river which deposited the 

 Danbury gravels had been cut down into lowland, and a fragment 

 of the bed had been left on the Danbury plateau in pre-Glacial times. 

 The Danbury gravels accordingly date from a period when the relief 

 of Essex was very different from that of the present day. Hence, us 

 the existing topography of Essex was pre-Glacial, and the Danbury 

 gravels were laid down long before its development, the Danbury 

 gravels are very long pre-Glacial. 



The determination of a more precise age for these gravels depends 

 on their position and the possible dates of introduction of their 

 constituents. The quartzites and black cherts have probably come 

 directly or indirectly from the Bunter pebble-beds of the Midlands. 

 Some of the gravel heaps in the Midlands, as near Worksop and 

 Nottingham, strikingly resemble those at Danbury owing to the 

 abundance of similar quartzites. I submitted in 1913 a typical 

 collection of Danbury pebbles to Professor Lapworth, Professor 

 Boulton, and Mr. Raw, who agreed that most, though not all of 

 them, could be matched in the Bunter pebble-beds of the Midlands. 



If these gravels are not Glacial, then, by whatever route they came 

 from the Midlands, they must have been introduced into Essex at 

 a date earlier than the denudation of the plain, 160 feet lower, which 

 now surrounds the Danbury hills. 



Various suggestions have been made as to the route by which 

 the foreign constituents in these gravels reached Central Essex. 

 According to Dr. A. E. Salter (1905, etc.), whose detailed study of 

 the composition of the gravels has thrown most important light on 

 their relations, the non-local constituents came from the west down 

 the Thames Valley or from the north-west across Hertfordshire through 

 the Stevenage Gap. According to others (e.g. H. B. Woodward, 1909, 

 p. 55) these quartzites and old cherts came from the south from the 

 Weald. Prestwich (1890, p. 146) suggested their derivation from 



