Shut off to the north and northeast by the Armenian range, to the northwest by the Taurus, Upper Mesopotamia retains, for a considerable extent, and especially on the eastern side, a rugged aspect.

The Kurdish mountains run close to the Tigris' bed for some distance below Mosul, while between the Tigris and the Euphrates proper, small ranges and promontories stretch as far as the end of the Taurus chain, well on towards Mosul.
Below Mosul, the region begins to change its character.

The mountains cease, the plain begins, the soil becomes alluvial and through the regular overflow of the two rivers in the rainy season, develops an astounding fertility.

This overflow begins, in the case of the Tigris, early in March, reaches its height in May, and ceases about the middle of June.

The overflow of the Euphrates extends from the middle of March till the beginning of June, but September is reached before the river resumes its natural state.