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] inches in depth. The Pimas do not practise rotation of crops, the soil being so rich from silt which is periodically deposited by the river at flood stage that the idea of exhausting it has never occurred to them.

Irrigation was practised for unknown centuries by the Hohokam, and the course of their great canals can yet be traced for miles, not only along the river bottoms, but also across the mesas where the large water-worn pebbles bound together with caliche or deposited lime must have required infinite labor for their construction. At the first appearance of the Pimas it may be presumed that they used the canals already constructed by their predecessors, hence they would be dull indeed if they could not maintain irrigation systems sufficient for their needs. The testimony of the early writers is to the effect that they possessed canals larger than they required and that the water flowed away from the fields in volume scarcely diminished from that at the head gates. The Gila has a uniform fall of 8 feet to the mile at this place, while the canals need not have more than 2.

As the water of the Gila and Salt rivers is strongly impregnated with alkali it tends under certain conditions to deposit salts in such quantities that the land is rendered unfit for use. The alkali rises to the surface in an efflorescence that resembles snow in appearance. From early descriptions of the country we learn that alkaline deposits were known while the tribe was yet under purely aboriginal conditions.

The Pimas knew, however, how to deal with this difficulty—they flooded the tract repeatedly and in this way washed the alkali out of it. They declare that they never abandoned a piece of ground because of it.

No very reliable estimate of the total amount of lend cultivated by this people has been made. Each family cultivates from 1 to 5 acres. With an abundance of water and the new needs of the tribe it is probable that the size of the individual holdings will rapidly increase. The farms are rectangular, arranged with reference