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THE GEOLOGY AND SCENERY OF THE CLUB'S 

 VOYAGE FROM MALDON TO CHELMSFORD, 

 AUGUST 8th, 1891. 



By T. V. HOLMES, F.G.S. 



\_Read August Sth, iSgi.'] 



TT is now three years since our very pleasant voyage on the 

 -*■ Blackwater estuary, from Maldon to the sea off Mersea, took 

 place. On that occasion we sailed (or were becalmed) on a broad 

 sheet of water having low shores composed of London Clay, gravel 

 or alluvium. During our voyage to-day we are towed along a 

 narrow stream, the banks of which are bright with flowers, through a 

 rich valley, bordered by hills of considerable height. At Maldon we 

 leave behind us the broad tract in southern and south-eastern Essex 

 which is wholly, or almost entirely, free from Glacial Drift, and enter 

 the district in which that formation covers almost the whole of the 

 surface, except that occupied by the valleys of the various rivers and 

 streams. In these valleys the underlying beds appear, that which 

 everywhere exists beneath the Glacial Drift and the Valley Deposits 

 during our course to-day being the London Clay. Indeed, could we 

 prolong our voyage up the Chelmer as far as Dunmow, or ascend the 

 other streams, which, when united with the Chelmer, form the 

 Blackwater, as far as Braintree or Coggeshall, we should still find 

 London Clay in the sides of the river-valleys, and Glacial Drift 

 capping the plateaux between them. In this district the Glacial 

 Drift generally consists of gravel covered by Boulder Clay, as we 

 saw during our excursion to Rainsford's End and Writtle on the nth 

 of July. Sometimes, however, the gravel is absent, sometimes the 

 Boulder Clay ; and more rarely, as in the new railway cutting at 

 Maldon, a little Boulder Clay may be seen underlying the gravel. 

 The full thickness of the London Clay in Essex is perhaps 450 feet, 

 but of course this is only attained where it is capped by the conform- 

 able Bagshot Beds. Where it is covered by the highly unconformable 

 Glacial Drift, as between Chelmsford and Maldon, or is exposed at 

 the surface, as between Brentwood and Rayleigh, its thickness is 

 much less. Thus, beneath Valley Gravel, near Maldon railway 

 station, were 130 feet of London Clay, there being 21 feet of 

 gravel. And at Maldon Waterworks the London Clay is said to 



