The Deyrah Dhoon, or, perhaps, more properly, Dehra Dhoon, is a valley cut off from the Dooab of the Ganges and Jumna by the Sevallic range of hills (average height about 2000 feet), which runs from the Ganges, at Hurdwar, in a north-westerly direction to the Jumna. Parallel with this range, to the north-east, is the first blue range of the Himalayas, on which Mussoorie and Landour are situated. Between these ranges, which are at an average distance from each other of about eight miles, lies the valley of the Dhoon. The bases of the hills, and a portion of the valley adjoining them, on each side, are covered with forests of very valuable timber. The centre of the valley, along its whole length, is open, with one trifling exception; and, where not cultivated, is covered with grass jungle, and a sprinkling of trees, both solitary and in clumps or belts, which, from a distance, gives the country a most park-like appearance. The town of Deyrah, and the cantonments of the Sirmoor battalion, stand in the middle of the valley, where it is intersected in its length by a road from the Ganges to the Jumna, and in its breadth by another from the plains of Indus, (through the Sevallic range,) to the Sanatorium of Mussoorie and Landour. The latter is fourteen miles from Deyrah, (half of which is ascent, the depôt being about 6300 feet above the valley,) and 7500 feet above the level of the sea. The water-shed, called here “pani dal,” also is near Deyrah, and streams rising on the one side of it run to the Ganges, on the other to the Jumna. These streams are large, increasing as they get nearer to the great rivers; very pure and clear; and, being of considerable rapidity, are well calculated to turn machinery, or to be turned out of their channels to irrigate the country as they pass.