THE 



GEOLOGICAL MAGAZINE 



NEW SERIES. DECADE VI. VOL. II. 



No. XII— DECEMBER, 1915. 



OZRIGKEnsr-A-X.. _A.:RT I CITIES. 



I. — The Danbury Gravels. 

 By Professor J. W. GREGORY, D.Sc, F.R.S. 



DANBURY stands on a gravel-capped plateau in Mid-Essex, five 

 miles east of Chelmsford. The .gravel is part of a once larger 

 sheet and contains a variety of rocks foreign to the district. It was 

 therefore naturally at first regarded as a glacial gravel. This view 

 was adopted hy S." V. Wood, jun. (e.g. 1867, p. 12; 1870, p. 61), by 

 the Rev. 0. Eisher (1868, p. 98), on the Geological Survev Map 

 (Sheet 1, N.E., 1871), and by Mr. Whitaker (1889, p. 279). 

 Sir Joseph Prestwich regarded the Danbury gravels (1890, p. 135) 

 as Bagshot pebble-beds invaded by some glacial agent, and the late 

 H. B. Woodward (1903, p. 15) described them as the wreck in 

 Glacial times of an older gravel. 



Objection has, however, been often taken to the glacial origin of 

 these gravels, as by Erench (1891, p. 211). They lack the structural 

 features and constituents which in this district are characteristic of 

 glacial deposits. In recent years the conclusion has been widely 

 adopted that these gravels are fluviatile in origin and pre-Glacial 

 in age. 



The Danbury gravels lie on a plateau of London Clay at the level 

 of from 300 to 360 feet O.D. They are in situ upon the surface of 

 the plateau at Danbury and on the ridge going north to Little 

 Baddow. They are there exposed in occasional natural outcrops, 

 and in gravel-pits to the south of Danbury Church and to the east of 

 the road to Little Baddow, about a mile north of Danbury Church. 

 Redeposited Danbury gravels occur on the slopes of the Danbury 

 hills; and at still lower levels they are mixed with material from the 

 glacial beds. 



The most striking feature of the Danbury gravel is its high 

 proportion of quartzites which are foreign to the district. These 

 quartzites include the liver-coloured saccharoidal variety, pink, 

 yellow, white, and black quartzites, varieties seamed with secondary 

 quartz-veins, some brecciated quartzites, and some which are merely 

 quartzitic sandstones. The series also includes jasperoids which pass 

 into compact red siliceous shales and black cherts. 



One of the rarest rocks found in the Danbury gravel is chert from 

 the Lower Greensand, though it is so abundant in the lower level 

 gravels of South-Eastern Essex. Prestwich recorded chert at Danbury 

 (1890, p. 135), and he generally used that term for the Lower Green- 

 sand chert; lie remarked, however, that it is more abundant in the 



DECADE VI. — VOL. II. — NO. XII. 34 



