280 Mate — Drift Deposits of the Eastern Counties. 



memoir on the drift deposits of tlie neighbourliood of Manchester, 

 it will be seen that the correlation of the individual subdivisions is 

 utterly hopeless. K, for example, the StrethUl Severn Valley 

 Section, v^here there is the unusual consecutive thickness of 210 

 feet, is compared with the full series given by Mr. Hull in tlie 

 neighbourhood of Manchester, it will be found that there is no 

 possible correspondence in lithological subdivisions. At Strethill 

 there is bu.t one Boulder-clay separating two masses of gravel, and 

 in the Manchester district one sand and gravel bed intervening 

 between an upper and lower Boulder-clay. Both series seem to 

 have about the same range with reference to sea level, but to bring 

 them into possible correspondence as to lithological subdivision, it 

 must be assumed, not only that one of the Manchester Boulder- 

 clays is absent in the Severn Valley, but that one of the Sevei'n 

 Valley gravel beds is missing at Manchester. These changes will, 

 however, be more easily explained by recognising the extreme local 

 character of the great mass of the materials making up the drifts, 

 and consequently the continual variation of their lithological condi- 

 tion, depending on the sources of materials and the local circumstances 

 of surface contour under which each was deposited. 



The extreme uniformity in the mineral character of the higher 

 Boulder-clay of the Eastern Counties is remarkable, and contrasts 

 with the varying composition of the drifts in other parts of the 

 kingdom. The fact that there is nowhere to be found, on the imme- 

 diate coast, such a thickness of drift as frequently occurs on the 

 higher ground, seems to render it probable that the comparatively 

 uniform terrace of clay, fringing the coast, was deposited during a 

 limited submergence, when the coast outline differed little from 

 what it is at present. If the coast clays and drifts are merely a 

 seaward prolongation of those occurring at much higher levels 

 inland, it seems difficult to account for its never capping the coast 

 cliffs of the older formations that exceed 200 feet in height, and if it 

 is the same drift on the coast that rises within a few miles (as for 

 example on Moel Tryfan) to more than 1000 feet, it would be ex- 

 pected to rise over the older formations on the coast cliif line, and 

 if the coast clay is older than the drift on the higher ground, how is 

 it that the higher is not superimposed on the lower, forming a 

 collective mass somewhat approaching the height of the inland drifts 

 superimposed on the older formations? Another point to be 

 noticed is, that the fringing terrace of clay is often present (as for 

 example on the Yorkshire Coast) along the coast where the adjacent 

 higher ground is driftless. In connection with this point may be 

 noticed the occurrence of erratic boulders at Pagham and along the 

 coast, west of Bognor, Sussex, the ground a little above the coast 

 line being entirely without drift; indeed, nearly the whole coast 

 circuit afibrds evidence of this limited submergence. The driftless 

 area of Devonshire is on the south coast fringed with gravels, which 

 seldom reach more than 150 feet above the sea, and on the north the 

 great deposit of clay and an underlying gravel bed, near Fremington 

 and Barnstaple, betokens a similar limited amomit of submergence. 



