BIRCH GROVES OF EPPING FOREST. 85
The result of the presence of humous compounds in the soil
is the formation of pan, a hard layer of sand, at about the level
of the normal water-table. The roots of trees cannot penetrate
this. Leaching of the soil and the formation of moor-pan effec-
tively prevent the rejuvenation of woodland.
Those who have known intimately, for at least thirty years,
the woodland of the Forest plateau have had the unique oppor-
tunity of witnessing there a period of transformation similar
to that which all woodland upon sand or sandy gravel undergoes,
sooner or later, in the course of its history.
It is generally conceded that birches have added greatly
to the sylvan beauty of the Forest, but should the great increase
in the number of these trees go on unchecked, the pleasure
derived from variety may in time be lost. Leaching of the soil
must inevitably continue while the present climatic conditions
persist. With this fact before us, in spite of the complete
cessation of indiscriminate felling under the present management,
and of the great reduction in the number of rabbits on the land,
we can hardly look forward in the distant future to a new birth
in the regeneration of the woodland upon the pebble gravel and
sand of the Forest plateau.
I take the opportunity to thank the following correspon-
dents : Mr. Gerald Buxton, Verderer of the Forest; Mr. F. F.
McKenzie, Dr. Edward J. Russell, Dr. W. G. Smith and Mr. J. M.
Wood, for valuable suggestions made during the preparation of
this address. Mr. Gerald Buxton also kindly invited me to
inspect the water-level of some wells on his estate.
"Fire-Brats" at West Ham.—Specimens of the little-known
Thysanurid, Thermobia furnorum, were found in June 1920, about a baker's
oven at West Ham, and are preserved in the Essex Museum at Stratford.
Bakers call these insects "fire-brats," because of their apparent fondness
for heat.
This species and Lepisma saccharina (the Silver Fish) are the only British
representatives of the family Lepismidae of the Thysanura. Thermobi
has not, hitherto, been recorded in Essex.—Percy Thompson.