125 
their lower surfaces, showing that they had been gently washed 
out of a neighbouring leaf bed to be redeposited, partially or 
wholly washed free from clay, in sand further down the river-bed. 
This could only have been done by a very gently flowing current, 
dissolving and washing the clay matrix in which they had lain 
whilst their structure was yet firm and undecomposed. Unfor¬ 
tunately these leaves can not be preserved, but crumble into the 
sand at a touch. A few yards further on current bedding was 
formerly evident, also clay beds, curved on the upper surface 
and overlayed by thin bands of lignite. Sometimes three or more 
of these, each separated by a thin band of clay, were seen curving 
over an old mudbank, and representing, probably, the effects of 
a succession of high tides near the ancient river-mouth. A section 
of the cliff, with measurements at about this point, is given by 
Mr. Gardner,* and it remains approximately correct at the 
present time. With slight modifications it is as follows :— 
ft. 
Plateau Gravel ... ... ... 5 
Boscombe Sands: 
Orange and Yellow Sand, about ... 20 
White Sand ... ... ... 14 
Estuarine and Marine Beds of Upper Bagshot: 
Irregular Clay and Clayey Sand, drab or 
ochreous ... ... ... 4 
Greenish Sand ... ... ... 2 
Light Grey Sand ... ... ... 15 
Lignitic Sand with redeposited leaves 
and small clay nodules ... ... 9 
Angular lumps of dark Clay in a matrix 
of light sand ... ... ... 13 
Dark Clay with pyritized stems and 
lignite ... ... ... 6 
Quartz Sand with clay seams ... ... 2 
Total ... 90 
At the point just described, and in many places where clay 
beds form the lower parts of the cliffs, a yellow or occasionally 
dirty white efflorescence is frequently seen covering the face of 
of the clay, sometimes over considerable areas, and even giving 
the appearance of a yellowish-green lichen. It crumbles to the 
touch, and disappears after rain, to re-form in dry weather. This 
has long been regarded as a deposit of ferrous sulphate, and it 
has been formed by decomposition of iron pyrites in the higher 
beds yielding a sulphate which uniting wtih organic matter in the 
lignitic clays, is then precipitated by evaporation of water on the 
surface of the cliff. At the last visit of the Geologists’ Associa¬ 
tion this appearance was very marked, and excited much interest. 
* Q.J.G.S. xxxv., pt. 2, p. 223. 
