As I was told so long ago, sitting in St James's School, the bench of mixed debris left after the Ice Age runs from Alexandra Palace to East End Road. Any gravel pockets left in it are permeable, allowing rain to pass through and emerge where the water reaches the clay joint as springs. The stream in Coldfall Woods starts as two springs on either side of Creighton Avenue, at about the same height as the lost Fortisniere Lake, and flowed northwards through Southgate. Springfield Avenue, again a few metres below the top of the hill, was not given its name for nothing. A stream arose south of Fortis Green, flowed south to about Woodside Avenue and then east, along the line of Fordington Road. From there it went through watercress beds in the unfortunately named Dirthouse Wood, which we now call Cherry Tree Wood, under the Great North Road and Bishop's Avenue to join the Mutton Brook.
For centuries this drainage pattern continued, but perhaps one day some early owner of Fortismere called in a 'Repton to make his estate more picturesque. Who he was, where he came from, or how he came to own the estate, we do not know, but the evidence of the map is clear. The lake in the 1894 map appears to be artificial, for no lake of this shape, in this position, could have been formed naturally. Nor when formed, could it have survived for long. The natural flow of the spring would have cut through the bank and drained the pond, since the force and persistence of streams are often astonishing.
Hampstead Ponds were formed to provide drinking water by damning a similar stream and digging out reservoirs. When no longer used for this purpose, a brickfield was dug higher up the slope, with stepped ledges all round where the clay was cut. The brickfield was abandoned and vegetation took over, producing, with the aid of judicious planting, a beautiful 'natural' pond, now called the Bathing Lake. By the 1980s it was becoming shallow, filled with decades of silt, so it had to be demudded. The water was drained out into a lower pond, floundering fish were captured in nets and transferred to a safe enclosure, and the bottom silt was revealed. There, running through the centre of the pond as it had done for centuries, was the old stream, cutting a clean path through the bordering mud. If the Bathing Lake had not been demudded, the silt would eventually have completely filled the pond and the stream would have reappeared on the surface.
The Fortismere Lake could not have been natural either: nor could it have survived for long without perpetual renewal. It has all the hallmarks of the romantic improvements so popular in the eighteenth and early nineteenth centuries. Probably whoever created the lake as a long narrow ribbon along the contour, half way down the slope, also planted a long screen-line of trees near the bottoms of Birchwood, Fortismere and Leaside Avenues. This line of trees, which is shown on the 1894 map, is more than a normal field hedge: in the centre is a circular interruption, perhaps a semicircular seat with a sundial in the middle, or a round summerhouse set in a clipped hedge. This semicircle is surely artificial, while the trigonometrical point nearby, shown as a triangle oii the map, cannot be older than the first Ordnance Survey about 1790, and may have been the reason for placing the semicircular feature just there. However old the pond may be, the screen of trees is surely an 'improvement' which Repton could have designed. He drew landscapes for his clients in his famous Red Books. A drawing showed the existing view with a folding flap to show what it would look like after the work was done. With these drawings he would beguile his patrons into spending untold sums of money to remodel their estates. The sketches shown on the next page can be seen as an imitation'Repton, showing Fortismere before and after the lake was created.