Botanical Report. 9 
northern edge of the Gault. The chief reasons which induced 
the Sub-Committee to adopt this district are as follows :—In 
the first place it is a tolerably large area (it comprises about 
500 square miles of land), it is also very compact, and is very 
well defined by natural boundaries. In the next place 
Croydon, as you will see from the one-inch Ordnance 
geological map, lies, as nearly as possible, in the very centre of 
this district. To the north, our town is distant from the Thames 
eight miles to Battersea, and ten miles to London Bridge, 
while from the edge of the Gault to the south it is also distant 
eight miles. It is also sixteen miles from the bend in the 
Darenth, which forms the extreme eastern boundary, and six- 
teen miles from the bend in the Mole, which is our extreme 
western limit. But above all, this district is very complete 
geologically, and therefore, necessarily, very complete for 
botanical purposes, plants being of course, dependent for their 
existence, to a great extent, upon particular soils. 
The strata which exist in the district are six in number, and 
when in their natural position, they occur in the following 
order :— 
Tertiary {Lesdon Beds. 
: London Clay. 
(Lower eocene). Lower London Tertiaries. 
Secondary. foe Greensand 
(Upper Cretaceous). con : 
Above these, and scattered about in no regular order, come 
the alluvial soil, which is, of course, at the top, and numerous 
surface beds of gravel, sand, and brick earth. As Professor 
Morris has very fully described the geological history of these 
strata in his lecture, it will not be necessary now to describe 
them more fully. 
The most important of them for our present purpose is 
undoubtedly the chalk. The strata which overlie it having 
been removed the chalk has become exposed over a large part 
of the district, that is, over that part of it which is uncoloured 
on the map, and which lies immediately to the S. S.E. and 
S.W. of Croydon. In the same way the Lower London 
Tertiaries, which are made up for the most part of gravels, 
sands, and clays lie exposed to the N.E., and they also form a 
line along the N. boundary of the chalk. The London clay 
lies exposed immediately to the N. and N.W., and one piece 
of Bagshot sand is found to the extreme W. Along the 
southern boundary of the district the Upper Greensand 
extends over a very small and narrow area, and below that, to 
the south, comes the Gault, which is a very stiff blue clay. 
