30 SPOLIA ZEYLANIGCA. 
slow process of subsidence, which, if continued, will result 
in another period of zoological isolation. It may well be that 
Adam’s Bridge was dry land until the dawn of historical 
times, and that the traditions of encroachments by the sea 
off Mannar and Colombo are founded on fact. 
Such are the recent geological changes which I have assumed 
in order to account for the distribution of our birds. 
But hypotheses which will suit admirably the distribution 
of one class of animals may not square at all with that of other 
orders. Further, as I said’ at the beginning of my Paper, 
birds are not nearly so sure a guide as mammals, while the 
differences between species are rather small distinctions upon 
which to form conclusions. As a counterbalance to these 
defects, the evidence regarding our Ceylon birds is fairly 
cumulative, and points persistently in one direction. 
The earth movements which I have assumed need not 
exceed a vertical measurement of 50 feet in either direction 
from the present level, and the change in climatic conditions 
during the glacial period is by no means wildly improbable. 
So I have hopes that my assumptions may not prove to be 
‘wholly empty theories. Indeed, they are more or less con- 
firmed by conclusions independently formed by Mr. Wayland, 
Assistant Mineral Surveyor, who has been investigating the 
river gravels in the valleys of the Kelani and Kalu-ganga. A 
few months ago, while the materials for my Paper were only 
half collected, and while my ideas were still rather nebulous, 
I sent him a short statement of the subsidence and re- 
elevation which I supposed might have taken place, and asked 
whether he knew of any geological evidence to support or 
disprove their existence. I received from him the following 
answer, of which he has permitted me to make use :— 
As far as I am aware, very little has been done with regard to 
the recent earth movements in the South of India and 
Geyion.).4.... 
Your letter came as a curiously unexpected confirmation of my 
own views with regard to the recent earth movements in this 
country. I have been paying some attention to the high level 
gravels of the Kelani Valley and of the Ratnapura District, and 
in order to explain the distribution, &c., of the gravels, I invoked 
a fairly large subsidence (something over 50 feet), which, according 
to my interpretation, probably increased in a N.N.W. direction. 
