Owing to the peculiar geographical conformation of the country, Quetta holds in her keeping all the approaches from the west, thus safeguarding Kalat. The Kalat fortress is only of minor importance as the guardian of the Mula stairway to the plains of India. It is the extraordinary conformation of ridge and valley which forms the great defensive wall of the southern frontier. Only where this wall is traversed by streams which break through the successive ridges gathering countless affluents from left and right in their course--affluents which are often as straight and rectangular to the main stream as the branches of a pear-tree trained on a wall are to the parent stem--is it possible to find an open road from the plains to the plateau. For very many miles north of Karachi the plains of Sind are faced by a solid wall of rock, so rigid, so straight and unscalable (this is the Kirthar range) as to form a veritably impracticable barrier. There is but one crack in it. For a short space at its southern end, however, it subsides into a series of minor ridges, and it is here that the connection between Karachi and Las Bela is to be found. These southern Las Bela approaches (about which there is more to be said) are not only the oldest, but they have been the most persistently trodden of any in the frontier, and they would be just as important in future as they have been in the past but for their geographical position. They are commanded from the sea. No one making for the Indus plains can again utilize these approaches who does not hold command of the Arabian Sea. In this way, and to this extent, the command of the Arabian Sea and of the Persian Gulf beyond it becomes vitally important to the security of India. Omitting for the present the Gomul gateway (the story of the exploration of which belongs to a later chapter), and in order to preserve something of chronological sequence in this book, it is these most southern of the Baluchistan passes which now claim our attention.