228 M. C. Rayner, W. N. Jones andj. W. Tayleur. 
up and distributed in the glacial period, much having been since 
removed by erosion (2). 
The deposit is a very local one, varying from a few inches to 
many feet in thickness, and is not always mapped in detail on the 
Drift Maps of the Geological Survey, but the contours of the areas 
occupied by Calluna often suggest the presence of clay-with-flints, 
and the present work confirms this. 
Chemical analyses of clay-with-flints soils from the South Downs 
shew that they are usually deficient in calcium carbonate, but the 
deep rather heavy loam which is found in the area under consideration 
would not appear at first sight likely to favour the growth of a 
typical heath plant such as Calluna vulgaris, in competition with 
grasses, etc. The soil conditions are, in fact, the reverse of those 
recorded by most authors as favourable to Calluna elsewhere. It 
seemed possible that some edaphic factor other than calcium 
carbonate might have a determining effect, since areas, apparently 
identical as regards exposure and physical characters of the soil, 
occur without Calluna. 
The present paper is preliminary to an attempt to investigate 
experimentally the causes determining the existence and spread of 
Calluna under the conditions described. 
A small area, bearing a well-defined patch of Calluna, has 
been mapped on a large scale (4 yards=l inch) and a number of 
excavations 4 feet square opened down to the chalk along two 
section lines X and Y (Fig. 1). 
From the data thus obtained, the thickness and distribution of 
the clay-with-flints were determined; the soil conditions were 
carefully noted, and samples removed for analysis. 
The mapped area lies on Upper Chalk between the 600 and 
700 feet contour lines on the ridge of Chalk Downs which forms 
the northward facing escarpment of the Hampshire Downs about 
six miles south-west of Hungerford. 
Along this ridge, from Inkpen Beacon, where it reaches a height 
of over 1,000 feet, westwards, the Survey Drift Maps do not record 
Fig. 1. Sketch-map, reduced from field-map, showing distribution of 
Calluna vulgaris on the area studied on Botley Down. The V-shaped marks 
indicate Calluna (single under 1 foot high, double over 1 foot high). The larger 
areas left blank are covered with grass. In the thick heather, indicated by 
continuous shading, grass does not occur ( e.g ., between holes Y 4 and YJ. 
Five small patches of Calluna exist to the right of Y 3 (just outside the 
map) between Y 3 and Y 2 . 
\J=Ulex europaus, C=Cratagus monogyna. X,, X 2 , &c., mark the position of 
holes. See Fig. 2 and Tables, 
