kt. M. Deeley—The Thames Valley Gravels. LE 
the position and extent of old shore-lines, and in the development of 
concealed coalfields, especially on outer ground where borings are as 
yet scarce, indications of the possible projection of pre-Carboniferous 
rock masses through the workable measures must be of great value. 
The information obtained by a petrological study of the sediments 
will thus be combined with that resulting from work on the mechanical 
composition, and with. the analysis of records of borings and their 
cartographical expression in the form of isopachyte systems and sub- 
surface contours. If the results obtained actually fall short of the 
above ideal, the method will still be justified. A few years ago 
Professor W. W. Watts wrote in his suggestive Presidential Address to 
the Geological Society (1911): ‘In order to obtain what Dr. Marr 
has called the ‘ geogram’ of a formation in its greatest perfection, we 
require to know the entire extent of its variations, not only along 
its outcrop, but in that part which is hidden from sight.’”? The 
whole of the section ought to be quoted, if space permitted, in this 
connexion. The methods of work detailed above help considerably 
towards the perfect conception of the ‘ geogram’ of a formation. 
(To be continued.) 
TV.—Tue Frovrio-cracta, Gravets or tHE THames VALLEY. 
By R. M. DEELEY, M.Inst.C.H., F.G.S. 
(Concluded from the February Number, p. 64.) 
T about 55 miles we reach the Hendon Lobe fan. At Dollis Hill 
the base of the fluvio-glacial beds lies at a height of about 200 feet, 
whilst their upper limit at Hendon is about 280 feet. On Finchley 
Hill to the north-east the Boulder-clay lies between the levels of 
240 and 340 feet. This was a small lobe, and the fluvio-glacial fan 
may have sloped rapidly towards the fluvio-glacial gravels of the 
main stream. On the section, Fig. 2, the heights are shown without 
_ correction for slope towards the River Thames. 
Where the Lea and Roding Valleys join the Thames Valley, and to 
the east as far as Hornchurch, the ice reached the fluvio-glacial 
gravels of the Thames. West of Woodford, at 43 miles, gravel caps 
the watershed between the Lea and Roding. Here the height of the 
deposit varies from 200 to 210 feet. 
That the Boulder-clay should occur here as low as 80 feet above 
O.D. is very interesting, for it shows that, as at St. Albans, the 
fluvio-glacial gravels must have been piled against the ice face and 
buried its end in places. Indeed, as the lower Thames is reached 
the evidence favours the assumption that in pre-Chalky Boulder-clay 
time the valley was perhaps within about 80 feet of its present depth, 
and was subsequently filled with a deep mass of fluvio-glacial gravel, 
a view, as previously stated, held by Pocock. 
At Dartford Heath, 22 miles, the gravel is from 90 to 140 feet 
above O.D. The upper portion of this deposit locks like a schotter 
formed by braided streams ; but the lower portion is a clean current- 
bedded gravel and sand, such as an ordinary river might form. 
The fossiliferous gravel at Greenhithe and Swanscombe, like the 
Dartford Heath deposit, lies within the upper and lower limits of 
