342 PLEISTOCENE GEOLOGY OF THE THAMES VALLEY. 



False bedded material here and there occurs and traces of 

 slight contemporaneous erosion in the form of little filled up 

 channels are sometimes exhibited by the sections. We have 

 obtained many boulders of Wealden or Purbeck ironstone with 

 Cypyides from the gravels in this pit, also a boulder of basaltic 

 rock, and some pebbles of "schorl-rock." Large sarsens, 

 which may be seen in situ in the Thanet Sand of the district, 

 likewise occur, some of them weighing many hundredweights. 

 In this pit many of the seams of gravel and sand are stained 

 with a hydrous dioxide of manganese, the staining following the 

 dip of the false bedding, and hence proving that the manganese 

 owes its present position to contemporaneous fluviatile deposi- 

 tion (70). 



(b.) A little to the east of Chalk Pit Farm, at the fork of 

 the two roads, an old gravel pit shows a few feet of gravel 

 similar to that of Sockett's Heath. 



(c.) Hcvigiiian's Wood. Gravel is exposed here in an old 

 pit at the entrance to the wood. The junction with the Thanet 

 Sand is seen in the shafts of the " Deneholes." 



(d.) About a third of a mile from the north-eastern 

 extremity of Hangman's Wood by the side of the road leading 

 to Orsett, an old gravel pit shows about seven feet of gravel and 

 sand from which we have obtained implements. 



IV. MIDDLE TERRACE DRIFT. 



The Middle Terrace Drift of the Grays Thurrock area is 

 found extending in a long narrow strip of brickearth, sand and 

 gravel, commencing near High House on the west, passing 

 through West Thurrock and Grays Thurrock, and ending off to 

 the east of Little Thurrock. The continuity of this band of 

 Drift is broken for a short distance to the west of Grays, by a 

 deflection in the northern boundary line of the Holocene alluvium 

 which here cuts inland as far as the Chalk outcrop. Thus the 

 Drift is divided into two portions — a western and an eastern. 



The western tract, with which we shall first deal, has a 

 total length of about three miles. Numerous sections are afforded 

 by the cuttings for the tramways of the various chalk quarries 

 between Grays and Purfleet. 



