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 Rh mountain Frontier may be qualified by a number of considerations arising from its physical structure. Of course a range or ridge with a sharply defined crest is the best of all. But sometimes the mountain-barrier may be, not a ridge or even a range, but a tumbled mass of peaks and gorges, covering a zone many miles in width (for instance, the breadth of the Himalayas north of Kashmir is little short of 200 miles), and within this area the inhabitants may be independent or hostile. Such has been the case with a large portion of the Pathan Frontier of India, where the physical conformation of the border lends an immense advantage to the holders of the mountains against the occupants of the plains. The desire to counteract this advantage and to transfer it to the Cis-border Power has led to the pursuit of what is known as the Scientific Frontier, i.e. a Frontier which unites natural and strategical strength, and by placing both the entrance and the exit of the passes in the hands of the defending Power, compels the enemy to conquer the approach before he can use the passage. It is this policy that has carried the Indian outposts to Lundi Khana, to Quetta, and to Chaman, all of them beyond the passes, whose outer extremities they guard.

In every mountain border, where the entire mountainous belt does not fall under the control of a single Power, the crest or water-divide is the best and fairest line of division; for it is not exposed to physical change, it is always capable of identification, and no instruments are required to fix it. But it is not without its possible drawbacks, of which the most familiar is the well-known geographical fact that in the greatest mountain systems of the world, for instance, the Himalayas and the Andes, the water-divide is not identical with the highest crest,