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Persia and BaMchistan predominate throughout the year.
The scanty cultivation on the hills is dependent on thewinter snows, or the rare showers which reach them from theeastward, or the supply of the larger local streams. Thelower plains would be uninhabitable but for the fertilizingirrigation furnished by the great river that traverses them.
At the foot of the great Himalayan barrier, and separating itfrom the more ancient land which now forms the highlandsof the peninsula, a broad plain, for the most part alluvial, Indusstretches from sea to sea. On the west, in the dry region, P ,ain -this is occupied partly by the alluvial deposits of the Indusand its tributaries; partly by the saline swamps of Kachchh (Cutch), and the rolling sands and rocky surface of the desert The greatof Jaisalmer (Jeysulmere) and Bikaner; and partly by themore fertile tracts to the eastward. Over the greater part ofthis region rain is of rare occurrence; and not infrequentlymore than a year passes by without a drop falling on theparched surface. On its eastern margin, however, in theneighbourhood of the Aravalli Hills , and again in theNorthern Punjab , rain is more frequent, occurring both inthe south-west monsoon, and also at the opposite seasonin the cold weather. As far north as Sirsa and Multan , theaverage rainfall does not much exceed 7 inches.
The alluvial plain of the Punjab passes into that of the GangeticGangetic valley without visible interruption. Up or down this P laln 'plain, at opposite seasons, sweep the monsoon winds, in adirection at right angles to that of their nominal course; andin this way the vapour brought by winds from the Bay ofBengal is discharged as snow and rain on the peaks and hill-sides of the Western Himalayas. Nearly the whole surfaceis under cultivation; and it ranks among the most productiveas well as the most densely-populated regions of the world.
The rainfall diminishes from 100 inches at the south-eastcorner of the Gangetic delta to less than 30 inches at Agra and Delhi , and there is an average difference of from 15 to25 inches between the northern and southern borders of theplain.
Eastward from the Bengal delta , two alluvial plains stretch Easternup between the hills that connect the Himalayan system with Bengal ,that of the Burmese peninsula. The first is that of Assam andthe Brahmaputra , long and narrow, bordered on the north bythe Himalayas , on the south by the lower plateau of the Garo,
Khasi, and Naga Hills. The second, or Sylhet and Cachar valley, is chiefly occupied by swamps and jhils, and separates