THE 



GEOLOGICAL MAGAZINE. 



No. XXXIII.— MAKCH, 1887. 



I. — On the eelative Ages of the Coast Botjldee-clay oj 



THE Eastern Counties, and that on the HiaHER Ground. 



By George Maw, F.G.S., etc. 



THE discussion on Mr. Boyd Dawkins's paper, " On the age of 

 the Lower Brick-earths of the Thames valley," at the meeting 

 of the Geological Society of London, 9th of January^ induces me to 

 submit a view of the relative ages of the Boulder-clays of the east of 

 England, which seems to bring into harmony the views of Mr. Daw- 

 kins, and the physical evidence suggested in the discussion that 

 seemed to conflict with them. 



Mr. Dawkins' opinion that the lower deposits of Brick-earth at 

 Grays' Thurrock, Crayford, and Erith were super-imposed by a 

 Glacial deposit containing transported materials, was objected to 

 on the grounds that they occur in a valley apparently excavated 

 after the deposition of the Boulder-clay capping the high land to 

 the north of London — implying an interval between the Muswell 

 Hill Boulder-clay, and the supposed Glacial deposits of the Thames 

 Valley, represented by the entire excavation of the valley, and the 

 deposition of the Brick-earths and gravels, containing mammalian 

 remains, underlying the Glacial beds. 



The most obvious explanation seems to be the recognition of such 

 an interval, and the object of the following remarks is to endeavour, 

 by a comparison with the Glacial deposits of the Eastern Counties, 

 to show its probability. 



The Boulder-clay of the Norfolk and Yorkshire coast (a and b, 

 Fig. 1), ranging from the sea level to a height of 50 to 100 feet 

 above high- water-mark, is generally admitted to be of a different 

 age to that (c) which forms the highest ground in Suffolk, 

 extending inland over a great part of the Eastern Counties, and 

 attaining a height of more than 200 feet above the sea. The two 

 deposits differ considerably in physical character. That on. the 

 lower level, commencing at high- water-mark with tough clays (b), 

 and transported materials, and graduating upwards at from 30 to 50 

 feet above the sea level, into highly contorted and quickly alternating 

 1 See Geological Magazine, No. 32 (February) p. 79. 

 VOL. IV. — NO. xxxiii. 7 



