; Drift Deposit at Carshalton. 289 
large a place) and just westward of The Park, whence the ground 
rises very slightly in that direction. 
One point of interest in the sections is that they prove an 
error of omission on the Geological Survey map (sheet 8), for 
this particular part of which I am myself answerable. No twinge 
of conscience, however, comes over me for the error, and for at 
least two reasons: firstly, that it was committed many years 
ago; and secondly, because when committed there was practically 
no evidence to lead one to map Drift over this tract, and conse- 
quently it was left as London Clay, which formation certainly 
occurs at no great depth all over (or rather all under) the tract. 
The. deposit which has been found to form the surface is 
indeed of a kind that. one had no reason to expect before the 
ground was opened. The Drift known in this neighbourhood 
was gravel, and, in the absence of anything to show the presence 
of gravel, Drift would not be mapped. The occurrence of sandy 
and loamy soil would not be taken as enough to justify the 
mapping of Drift, as such a soil might occur locally in a London 
Clay district. It was not indeed until the presence of sand over 
the surface was proved by trial that this ground was thought to 
be fitted for a sewage-farm, a purpose for which of course clay is 
not exactly suited. I believe that our member, Mr. Baldwin 
Latham, was as surprised as I was at finding so good a site in 
so handy a place for his work. 
The above remarks are made merely to show some of the 
* difficulties of mapping Drift, and not in the least to gloss over 
the faults of former years. I am far too old a geologist to feel 
the least shame at making a mistake, especially one of omission. 
At my first visit to the works I roughly sketched, on the six- 
inch map, a possible boundary for the Drift here, limiting it to 
the higher ground, as a separate patch; but later visits have 
given further evidence of the extent of the deposit, showing it to 
extend eastward down the gentle slope until it joins the gravel of 
the lower ground. It will be convenient therefore to notice all 
the sections that have been seen at various times. 
All the excavations seen show the presence of a mantle of 
sand, for the most part stoneless, though here and there a few 
flints occur in it. The boundary of this sand is mostly difficult 
to trace; but at two points, on the north, it was made fairly 
clear. Along the lane that forms the eastern border of the ground, 
_ the ditch (for the outfall) is in sand up to about the north-western 
corner of The Park, by the track to The Limes (E.N.E.), whilst 
at that spot the London Clay rises up to the surface. Again, 
about a sixth of a mile W.S.W. from this spot, in a slight hollow 
of the ground, there is peaty earth, caused by the damp springy 
nature of the ground, which results from the throwing out of 
water from permeable beds above by the London Clay below, 
