GEOLOGY OF HAMPSTEAD HEATH
The higher parts of Hampstead town and all of Sandy Heath and West Heath are an outcrop, up to 25m thick, of Bagshot Sands, ( named after the deposit first found in West Surrey.)
This marks the course of an ancient river and granite particles have been discovered from Devon.
In some places the sand appears coarse yellow, while in others it is finer and light in colour, mixed with loam and sandy clay.
There are at least 90m of London Clay, which is rich in fossils.
Beneath these layers lie the Woolwich and Reading Beds, Thanet Sands, Upper and Lower Chalk, Chalk Marl and Gault.
In places the sand and gravel rest on spongy ground from which issue Hampstead’s many springs.
Each layer has its own identity with the uppermost layer being sand deposit, with some deposits of pebble gravel, rising 420 feet above London.
This geology extends from the upper part of Fitzjohn's Avenue, arcing along the Spaniards Road and Hampstead Lane.
The sand is fine-grained, rich in iron salts and coloured from buff to deep orange.
The geology creates acid soils and low agricultural usefulness but the sand proved good for local roadworks, etc!
Gravel has been excavated for many years from such places as near Whitestone Pond and, of course, Sandy Heath.
Sandy Heath is now covered with trees but the potholed surface is still visible. (see photo above)
It is interesting to note that, before sand excavations started, Sandy Heath was level with the Spaniards Road!
Because of the nature of the Claygate beds, water moves horizontally and can be seen seeping/springing out of the sloping areas.
Another example of water seeping out of the meeting of Bagshot Sand and Claygate Beds is the small stream on the Kenwood Pasture Land, which is above the Wood Pond.
Underfoot, the walker is one moment treading on firm ground and the next on muddy areas as a result of this.
Changes in the flora tend to correspond with these areas so that fine-bladed grass and acid-growing plants give way to coarser and darker grasses of the clayish, moister soils.
This variability is shown in such areas as Kenwood's Sphagnum Bog.
Elsewhere, these patches are often frequented by yellow iris and water mint.
The lower parts of The Heath, such as Parliament Hill Fields and the Heath Extension are on London Clay.
These are on the richer, neutral soils of the Claygate Beds and London Clay and were, in fact, never true heathland.