14 



mapped out broadly by the Geological Survey/'^ but there is 

 yet much work to be done in the way of filling in details, 

 especially with regard to the Drift and other superficial 

 deposits. Geologically considered, our district is compara- 

 tively modern, the oldest forjnation being the chalk which 

 crops out on the Essex shore of the Thames about Purfleet, 

 and extends to just beyond Little Thurrock, a distance of 

 some five miles in an easterly direction. Overlying this strip 

 of chalk at its eastern extremity there is a detached patch of 

 Thanet sand. A line drawn across from Grays Thurrock to 

 Stifford, the northern limit of the chalk at about its widest 

 part, would be nearly one mile and three-quarters in length. At 

 Bishop Stortford the chalk again appears. The thickness of this 

 formation in the London Basin is from over 600 to more than 

 1,000 feet ; a boring carried do^\m into the Ganlt at Loughton 

 Station gave a thickness of about 690 feet, and at Harwich a 

 boring to a depth of 1,042 feet carried down into strata below 

 the Gault showed the chalk to be 888 feet thick. Cretaceous 

 fossils have been obtained in some abundance from the chalk 

 pits at Grays and Purfleet. By far the larger portion of our 

 county stands on the tertiary formations above the chalk. Of 

 the Lower Eocene series the Thanet Sands are present in a 

 broken band of about one mile in width at its widest part, 

 and of an average thickness of about thirty feet, which crops 

 out to the north of Purfleet, and following the chalk extends 

 eastward along the valley of the Thames. The chalk pits at 

 Purfleet and Grays show well the junction of the two forma- 

 tions. Next in order above the Thanet beds we have the 

 Woolwich and Reading beds following the former, as a narrow 

 strip commencing about Wennington and extending eastwards 

 to Stifibrd, where the strip commences to broaden out, and 

 another patch of the same beds is found about Stratford and 

 West Ham, to the east of the alluvium of the Lea valley. 

 The Woolwich and Reading beds have an average thickness of 

 about fifty feet. The uppermost member of the Lower Eocene 



* In making the following rough sketch of the geology of the county I 

 have largely availed nwself of the admirable publications of Mr. W. 

 Wliitaker, of H.M. Geological Survey, as well as of the maps published 

 by the Survey. 



