I may here mention that the Peruvians actually carried their irrigating streams in tunnels through hills of solid rock.

Mr.Gill told me he had been employed professionally to examine one: he found the passage low, narrow, crooked, and not of uniform breadth, but of very considerable length.

Is it not most wonderful that men should have attempted such operations, without the use of iron or gunpowder?
Mr.Gill also mentioned to me a most interesting, and, as far as I am aware, quite unparalleled case, of a subterranean disturbance having changed the drainage of a country.

Travelling from Casma to Huaraz (not very far distant from Lima), he found a plain covered with ruins and marks of ancient cultivation but now quite barren.

Near it was the dry course of a considerable river, whence the water for irrigation had formerly been conducted.