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MR. T. V. HOLMES ON SECTIONS BETWEEN 



and Upminster rarely exceeding 9 to 10 feet in depth ; and they 

 show gravel, almost wholly, south of ISTorth Ockeudon, and loamy 

 beds thence to Crauham Hall, as depicted on the map of the Geolo- 

 gical Survey. 



In the cutting west of Upminster station and east of the Ingre- 

 bourue London Clay appears, capped here and there somewhat 

 irregularly by a variable amount of gravel or loam, the former 

 predominating. The gravel is seldom more than 6 to 7 feet thick 

 in this cutting, and its base is from 85 to 90 feet above Ordnance 

 datum. It therefore belongs to a higher terrace than that of the 

 plateau between Cranham Hall and the Mardyke. And on crossing 

 the Ingrebourne we find that the sand and gravel capping the sur- 

 face of the ground along the course of the line north of Hornchurch, 

 and thence to the junction with the Great Eastern Railway at liom- 

 ford, belongs to this same terrace, which is the highest and oldest of 

 the Thames Valley deposits in this district. 



As might be expected from its greater age, this highest terrace 

 occupies a much more limited area than the lower terraces of later 

 date which occupy the ground between Hornchurch and Komford on 

 the north and Barking and Eainham on the south. And its character 

 as an old river-deposit is not quite so evident at a glance as is that 

 of the lower gravels, on account of the much greater number of 

 valleys which have been carved in it as a consequence of its superior 

 antiquity. On the map of the Geological Survey this oldest terrace 

 is coloured as Thames Valley Gravel, but no attempt has been made 

 to indicate the boundaries of the various terraces. In fact no such 

 separation is practicable, inasmuch as the underlying formation, the 

 London Clay, is much too soft to show definite terraces for any 

 appreciable distance. The result of this state of things is that all 

 the old Thames Valley Gravel between the Lea and the Mardyke 

 might be supposed, from uniformity of tint and the absence of any 

 distinguishing signs, to consist of one sheet at a nearly uniform 

 level, though the height of its surface above Ordnance datum varies 

 from less than 20 feet to more than 100 feet. 



A railway journey from Barking to Hornchurch across this broad 

 expanse of old river-gravel is one of gradual ascent. At Barking 

 station the surface-level is rather below 20 feet. At Dagenham it 

 averages about 25 feet, and a mile beyond Dagenham it is about 

 30 feet. About three quarters of a mile south-west of Hornchurch 

 the railway runs through a cutting in gravel at a greater elevation, 

 the height of the surface at Hornchurch station being more than 

 60 feet. And on alighting at Hornchurch and turning northwards 

 it becomes obvious that, above the gravel and loam which have been 

 60 largely excavated south of Hornchurch station, there is another 

 terrace to which the gravel worked between Hornchurch Church 

 and the windmill belongs. This highest gravel-pit averages 14 or 

 15 feet in depth, and the gravel taken from it must have been almost 

 entirely above the 100-feet contour-line, as the surface at the church 

 is a little over 117 feet in height. But the boundary of this highest 

 terrace, though fairly well marked for a few yards near the wind- 



