312
THE ESSEX NATURALIST
banks split up the urban sprawl. The overall population of setts
in the area under consideration is much smaller, being 112 setts
in 600 sq. km. (230 sq. miles) or 1 sett per 5.3 sq. km. (2.05 sq.
miles). Of these setts only a proportion are occupied by badgers
at any one time.
Setts occur in the area between heights of 40 and 350 ft. OD
(12.2 m—105 m). As shown in figure 1 however, more setts
occur between 250-350 ft. (76 m — 105 m) than 40-250 ft. OD
(12.2 m — 76 m).
Correlation of Distribution with Geology.
In the area under study, setts occur in all the different geolo-
gical deposits. However, it is apparent from the map that there
is a general correlation of those areas with a dense distribution
of setts and those of certain geological deposits. That is to say,
badgers appear to have a preference for certain types of geolo-
gical deposit over other types. Most of the setts occur in the
regions where the surface geology is of a sandy nature, in parti-
cular the Bagshot and Claygate Beds which crop out in com-
paratively limited regions as compared to the much wider area
of the London Clay and the Boulder Clays. All the areas which
have a relatively dense distribution of setts within the region
have a similar sandy geological character.
Other areas of light terrain such as the sand and gravel
spreads of the Thames Terraces accommodate the majority of the
remaining setts. However, a certain number of setts are found
in other localities where clays predominate. But in these in-
stances the setts are isolated and never in well developed groups
as in the more favourable regions and are seldom active.
Figure 2 shows the soil characteristics for all the setts, re-
corded in the field. This information is taken from data recorded
by various people for the National Badger Survey. The figure
shows that only 14 setts were noted as being on pure clay soils,
compared with 99 in lighter sandy soils.