106 SPOLIA ZEYLANICA. 
river or sea sand is differently constituted, for, in addition to 
quartz, a large number of other minerals are present. Among 
these felspar 1s conspicuous. 
Felspar gradually decomposes under the influence of 
meteoric waters ; and one of the chief products of this break- 
down is kaolin (china clay), which takes the form of exceed- 
ingly minute flakes. But felsparis not by any means the only 
other mineral besides quartz, which is to be found in sands 
derived, as those of Ceylon are, from igneous and metamor- 
phic rocks. There are, besides, ferromagnesian silicates and 
iron ores, all of which are unstable. These decompose in time 
under the influence of rain water just as felspar does. 
In the light of these facts, therefore, we may interpret the 
redearth. In my opinion the red earthisa wind-borne deposit, 
of which the constituent grains were those of the crystalline 
rocks from which the particles were derived. In the course of 
time the unstable minerals have decomposed, thereby giving 
rise to the usual decomposition products, of which finely 
divided kaolin and hydrated iron oxide are the two most 
prominent. Thus can we account for the peculiar features of 
the red earth. 
I may say that certain deposits of white sand in the Western 
Province can be shown to be derived directly from the red 
earth. All the fine earthy material has been removed from it 
by natural causes, so that now it consists of over 99 per cent. 
of quartz sand. I find on estimation of sixteen samples that 
on the average 1°225 per cent. of the material is below one- 
ninetieth of an inch in diameter, a figure sufficiently close to 
that obtained from modern dunes to corroborate our con- 
clusion drawn from other facts. The wide occurrence of red 
earth points to the past existence of enormous stretches of 
blown sand, in fact to desert-like conditions over much of 
the low-country. 
Such, then, are the plateau deposits; now for their 
distribution. 
In the course of coast surveys I have traversed on foot the 
entire coast between Kumane in the south-east and Point 
Pedro in the north vid Galle, Colombo, and Mannar; and 
from Point Pedro to the mouth of lagoon immediately above 
