_THE GEOLOGY OF THE HEATH._
The appearance of the Upper Heath, as that portion of it beyond Jack
Straw’s Castle to the north-west is called, shows that the purchase of it
for the sake of its preservation was not a day too soon, while as far as
preserving the primitive beauty of the Heath, it was years too late.
The surface, originally flush with the paddock near the North End Hill,
has been delved by sand and gravel diggers into a series of pits and
hollows, with corresponding mounds and hillocks. At one period (1811),
owing to the multiplicity of building operations going on, upwards of
twenty loads a day passed through Hampstead, besides the quantity taken
away by other roads.
Looking at the ravaged Heath as it appeared in 1872, it would seem as
if this wholesale devastation had been going on ever since, without
reference to anything but the market value of the deep layer of gravelly
sand which geologists tell us overlays the Heath in places to the depth
of 80 feet. No doubt the barren appearance of the surface east of the
Spaniard Road and in the vicinity of the Vale of Health may be attributed
to the removal of this gravelly substratum till the clay was reached,
which formed the vari-coloured hillocks that used to make quite a
feature of this portion of the landscape. Subsequently, as we have seen,
the highest part of the Heath was treated as one huge gravel-pit, the
purchasers of which dug out their loads any and every where, encroaching
within my memory on the Fir-tree Avenue, in front of the historic houses
at Park Gate, as this entrance to the Heath continues to be called; and,
not content with delving it in the open, the purchasers were permitted to
ruthlessly dig out the sand from under and between the roots of the fine
old trees, undermining many of them, and leaving them a prey to the first
tempest.
In this way nearly all the trees on this part of the Heath have suffered;
and to this cause may be attributed the fragmentary condition of the
Stone Pine Avenue, and the curious exposition at one time of the efforts
of some of the remaining ones to support themselves by sending pile-like
roots into the ground on the side on which they are most exposed to
tempests. Fortunately for their existence, the Board of Works have taken
steps to preserve their weird beauty to the Heath, and protect the groups
of elm and ash and other trees, which so long as the season of leafage
and blossom remains to them will literally keep green the memory of that
lover of Nature, the planter of the majority of them, Mr. Turner, of
Thames Street.
Naturalists and geologists may still find here abundant materials for
their studies,[222] and the geology of Hampstead Heath would in capable
hands prove a most interesting chapter in its history. But the writer is
not a geologist, so must be content to summarise what others have said,
or written, of it.
Time was when a sea a hundred fathoms deep rolled over the present site
of London and the lands around it.[223] Evidence of its having been above
Hampstead Hill is found in the deposits it left on the summit of it.
On the highest part of the Heath there lies a horizontal bed of
light-coloured ferruginous sand, mostly coarse and gritty; but an
admixture of fine sand and thin bands of loam occurs in places, which,
like the sand, is destitute of fossils.
In the lowest part of the deposit it becomes more clayey, and passes
gradually to sandy clay, and eventually to the stiff blue clay called
London Clay. Many well-preserved fossils are found in the sandy clay,
which proves that the deposit was formed 50 fathoms below the sea-level;
while the fossils of the London Clay indicate a much deeper sea.[224]
The lowest portion of the sandy clay is known by the appearance of
swampy ground, and by the oozing out of the springs, as in Well Walk, in
Conduit Fields, and at North End. It is the property of clay to hold up
water, and the lower part of the sand, through which it percolates, lying
horizontally on the clay, and becoming very full, the water comes out at
the edges of the hill, especially at the places indicated. The sandy clay
leading down to the London Clay is about 50 feet thick, and from that at
Child’s Hill beautiful marine shells, quite perfect, showing that they
had neither been rolled nor drifted, were found at a depth of 30 feet in
an excavation for drainage in the Finchley Road (Child’s Hill, 1872).
Below this comes the stiff London Clay, about 350 feet thick.
The chalk at Hampstead Hill is another proof of its submarine formation.
This is many feet thick, and is pure carbonate of lime, composed of
minute sea-shells, and must have taken an immense period of time to form.
There have been found in it hard portions of animals similar to those
which now dwell in the sea. So many evidences exist around the British
Islands of change of levels, both by elevation and depression, that there
is no improbability in supposing that Hampstead Hill has through past
ages been gradually raised from below the level of the sea, and at times
has been again depressed, which change geologists believe to have taken
place more than once, the hill not taking its present form till after
several upheavals.
The changes of temperature must have been as vast as the geological ones.
Tropical animals—large elephants, rhinoceroses, hippopotami, etc.—are
said by Professor Owen to have inhabited the neighbourhood of Hampstead;
and though no evidence remains here of the glacial period, icebergs
floated at Finchley, and left their deposits in the shallows of the sea
that covered it, and doubtless at that period Hampstead was covered with
thick ice. The fossil nautilus, sharks’ teeth, and the plates and spines
of echini,[225] have frequently been found, the latter in gravel-pits
upon the Heath. Modern geologists have stated that the sand at the top
of the Heath is only a small patch, very irregular in shape, and that
there was another patch on the top of Highgate; and it is suggested
that perhaps these were formerly connected, but that the depression of
the ground at Caen Wood may have swept the sand from them. Park, on the
other hand, observes ‘that vast quantities of sand exist at Hampstead,
the Heath being covered with it at an average to the depth of 10 feet,
though in some places it is more than 25 feet in depth, notwithstanding
the length of time it has been supplying the Metropolis and intermediate
villages.’ Could both be thinking of the same stratum?
That the Heath is covered with sandy gravel (in fact, the Heath is
confined to the sand) is sufficiently apparent to the ungeological eye,
especially in this rugged and denuded portion of it. It has been a vexed
question with the artists and the conservators of the Heath whether to
fill up these irregularities of the surface or leave them to Nature’s
healing. Already, taking advantage of the past year or two’s rest from
aggression, she has covered the scarred places with her green mantle,
and crowding fronds of common brake have taken to grow on the graves
of its old habitat. Great spaces amongst the gravel-pits have been
brilliant with the glittering flowers of the common broom, and where the
unquenched springs still drain themselves into pools and shallows, stocks
of willow-wood have in some instances been driven, which have taken root
and put forth branches, and in a few more seasons will be vigorous trees.
Our hope is that the present conservators of the Heath, to whom great
praise is due for the visible improvement in its appearance, will be
patient with this seemingly most hopeless portion of it, and leave the
rest to the great Mother’s care. In time the rugged superficies will
round and soften, and the hollows be converted into bosky dells, tangles
of woodbine, wild-rose, and arching brambles. We have already seen
indications of the return of _Erica cinerea_ and _E. tetralix_, once
common on the Heath, and the tufted stems and silvery lilac flowers of
the indigenous heather.
If loving hands a little after harvest-time would bring an alms of hips
and haws and mountain-ash berries and drop them carelessly about the
turf, the birds would scatter them, and help to bring back beauty to
the Heath, that wild beauty that is Nature’s own, and, though quite
unpremeditated, is ever in agreement with its surroundings.
For the geological part of this chapter I am indebted to notes
taken of a lecture on ‘Hampstead Hill in Past Ages,’ delivered
by C. Evans, Esq., F.G.S., in Rosslyn Hill Schoolroom, March,
1872.