6 THK NEW RAILWAY BETWEEN UPMINSTER AND ROMFORD. 



have received a signal illustration in the Boulder Clay of the Horn- 

 church cutting. For, in the absence of special evidence to the 

 contrary, we may rightly assume that the gravel covering the Boulder 

 Clay at Hornchurch, which forms part of a higher terrace than that 

 traversed by the railway south of Upminster, belongs therefore to an 

 older one. Hence, if the Boulder Clay is evidently older than the 

 Hornchurch gravel, it must rightly be considered to be still more 

 ancient than the gravel nearer the Mardyke. Locally, the only 

 sound test of the Glacial or post-Glacial age of a bed is the nature 

 of its relation to the Chalky Boulder Clay of the district, and to 

 attempt to employ any other is but to introduce confusion. Of 

 course, the age of the Chalky Boulder Clay of Essex as com- 

 pared with that of any given deposit of the Glacial Period in 

 Lancashire, Scotland, or elsewhere, may rightly be a question for 

 discussion and speculation. But in Essex and Middlesex the 

 only standard of comparative age is that furnished by the local 

 Boulder Clay. 



It is then evident that if we may rightly conclude that the Horn- 

 church gravel is older than that at less elevation between Upminster 

 and the Mardyke, we are also justified in deciding that it is older 

 than the river deposits which occur at a lower level at Grays and 

 Ilford, or at Erith and Crayford on the Kentish shore. 



It is also obvious, that if we compare the Hornchurch gravel with 

 fluvial deposits fifteen or twenty miles higher up the course of the 

 river, we should expect to find its equivalent in beds with an eleva- 

 tion as much greater than that at Hornchurch as the fall of the river 

 per mile, when the gravel was deposited, would indicate. If, for 

 example, the average level of the Hornchurch gravel should be loo 

 feet, then, supposing a fall of one foot per mile, the equivalent terrace 

 fifteen miles higher up would be 115 feet, and so on. 



Thus the natural inference is that as the Hornchurch gravel is 

 older than the various river deposits of Grays, Ilford, Erith, and 

 Crayford, and the Chalky Boulder Clay is evidently older than the 

 Hornchurch gravel, the fossil remains found in the river deposits of 

 all the places just named are rightly considered to be post-Glacial. 

 The probable age of the Chalky Boulder Clay, as compared with that 

 of beds of Glacial age in Wales, Scandinavia, or elsewhere, is, as I 

 have already remarked, a wholly distinct question. In what is 

 termed the Glacial Period, glacial beds may well have been in process 

 of formation in the north of Scotland long after they had ceased in 



