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



lower level gravels. Dr. Salter does not record this chert from 

 Danbury, but he has lent me a small pebble he collected from the pit 

 to the south of Danbury, and a section shows that it is a Lower 

 Greensand chert, an identification kindly confirmed by Dr. Hinde. 

 I obtained a larger specimen (2^- by 2 by 1 inch) from a pit a mile 

 north of Danbury. The Lower Greensand chert is, however, 

 extremely rare in these gravels, whereas in the lower level gravels 

 of Southminster and Southend it forms from 6-14 per cent of the 

 pebbles. 



The Danbury gravels have so far yielded none of the felsites or 

 ' rhyolites ', which are found in the neighbouring lower level gravels, 

 as I have found them at Gay Bowers, to the south-east of Danbury, 

 at the level of below 200 feet. 



Another significant fact in the composition of the Danbury gravels 

 is the absence of Jurassic sandstones and of the large irregular 

 unrolled flint nodules, which are common in the Glacial beds and in 

 the post-Glacial gravels of the district. The' Glacial and post-Glacial 

 gravels also contain occasional pebbles of basalt, but I have never 

 found any in the Danbury gravel. 



The absence of Jurassic sandstones, large unrolled flints, and 

 basalt indicates that the Danbury gravels were deposited before these 

 rocks were brought into Mid-E6sex during Glacial times. 



The Danbury gravels are therefore free from the constituents 

 introduced during the glaciation of the district. 1 The structure of 

 the gravels also furnishes no evidence of their glacial origin. The beds 

 are often false-bedded, and they are sometimes contorted and have 

 pebbles standing on end ; but I have not seen anything in the gravels 

 which gives clear evidence of ice action. 2 The pebbles are never 

 striated ; their forms, though often faceted by wind action, are not 

 those characteristic of the glaciated stones in boulder-clays or 

 glacieluvial gravels ; the irregular bedding is of the kind due to rapid 

 currents of water, and the contortions may be explained by slipping 

 down the clay slopes and by movements during the consolidation 

 of the gravel. There appears to be no valid evidence for the glacial 

 origin of the Danbury gravel. It maybe objected that such evidence 

 is afforded by the association of boulder-clay with these gravels. 

 The Geological Survey map of the area (Sheet 1, jS~.E.) does not 

 mark any boulder-clay on the Danbury plateau, but it shows three 

 small patches at lower levels on the adjacent hill-slopes, where they 

 would be associated with redeposited Danbury gravels. I have not, 

 however, been able to find at these localities any boulder-clay or any 

 trace of it. Search for pebbles from the boulder-clay has been in 

 vain. The most probable locality of the three (north-west of Bassetts) 

 has been tested to the depth of two feet by a soil-sampler along a line 



1 My observations fully confirm those of Dr. Salter (1905, p. 31) as to the 

 absence of glacial debris from the Danbury gravels and its presence in the later 

 gravels along the existing river valleys. Wood (1867, p. 2) had remarked the 

 easy recognition of the post-Glacial gravels by the presence of material derived 

 from the Glacial beds. 



2 The eolithically chipped flints which Cunnington called ' glacioliths ' 

 indicate the action of severe frost, but not of glacial conditions. 



