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February, 1918. ] Annual Address. xix 
younger rocks, such as the Siwalik hills and the Tertiary 
tanges of the Kangra valley. 
Geographically, as well as geologically, India falls into 
three broad subdivisions—the Indian Peninsula on one side, the 
Himalayan system on the other, and, between the two, a broad 
belt of alluvial plain. The Peninsular area is composed of 
crystalline rocks of great age, and is one of the oldest land sur- 
faces in the world: the Himalaya, on the other hand, are, 
geologically speaking, a young mountain range, made up largely 
of rocks laid down under water and subsequently folded and 
raised from below the sea; they are, so to speak, the crumpled 
edge of the great plateau of Tibet. Still younger is the alluvial 
still being, carried down from the mountains by the great 
Himalayan rivers. Although we have no direct means of as- 
certaining the depth of this alluvial belt, both geological and 
Seodetic observations lead us to believe that its thickness in 
Places must be reckoned in miles ; it is shallow on the south, and 
*ppears to deepen gradually northwards to the foot of the hills, 
where it merges into its more or less immediate predecessors, the 
