STONE AGES OF CEYLON. 115 
determines the periods of geology by means of radio-activity,* 
were formed some fifteen hundred millon years ago, The 
sedimentary beds, practically unknown in this country till 
recently, are on this basis comparatively modern. 
How long the country of Ceylon has been above the ocean 
nobody can say ; but the extremely advanced stage of denu- 
dation of the mountains shows that many eons have passed 
since the rain first beat and the sun first shone upon this 
land. 
Doubtless all have seen that wonderful view from the Hapu- 
tale Gap, where one looks down upon the jungle across the tank 
of Hambagamuwa, and on to the sea 5,000 feet below and 40 
miles away. And beneath the general level of the range you 
must have noticed the remnants of a vast plateau, which now, 
battered and dissected by the ravages of time, stands out as 
hills and pinnacles from the forest-covered plains. From 
Haputale this plateau, or periplane, is best observed ; but it 
can be traced with more or less distinctness all round the 
mountain zone. It is a wonderful relic of a time long past 
when the blue ocean lapped the highlands of Ceylon. Below 
the level of the periplane, which I call the mountain plateau, 
is the remnant of another, infinitely younger, yet almost as 
old may be as the human race itself. Over this vast plain 
roamed savage man; perhaps a thousand centuries ago. 
The rivers began to carve their courses in the mountains 
before the periplane emerged ; probably they were hoary with 
age ere this event took place. That they had run for countless 
ages before the second periplane was formed is certain, for it 
can be shown that the former was dissected much as now 
when the plateau gravels were deposited. The rivers had 
taken their courses before denudation had carved away the 
less resistant portions of the mountain plateau, so that now we 
have the quaint anomaly of rivers cutting through hills instead 
of adopting easy routes around them.+ 


* Radio-activity and the Earth’s Thermal History, Part II. (Geol. 
Mag. N. S., Decade VI., March, 1915, Vol. II., pp. 102-112). 
+ For example, the Kelani-ganga above Hadduwa cuts through a 
high rocky ridge, thus detaching the end of it from the main mass. 
The Kalu-ganga flows through the range between Nambapana and 
Dumbara, 
