The dam of Red Lake is an elegantly modeled rib of metamorphic slate, brought into relief because of its superior strength, and because of the greater intensity of the glacial erosion of the rock immediately above it, caused by a steeply inclined tributary glacier, which entered the main trunk with a heavy down-thrust at the head of the lake.

Our streams, in spite of the millions of dollars spent upon them, are less navigable now than they were fifty years ago, and the soil lost by erosion from the farms and the deforested mountain sides, is the chief reason.

There has been, however, a considerable amount of erosion on the hills, and if, as seems likely, the water-works have been out of order for several centuries, it is not surprising that all traces of them have disappeared in places.

On a July morning in 1911, while strolling up the Ayahuaycco quebrada, an affluent of the Chunchullumayo, in company with Professor Foote and Surgeon Erving, my interest was aroused by the sight of several bones and potsherds exposed by recent erosion in the stratified gravel banks of the little gulch.

Topsoil is lost through erosionwind erosion, water erosion, erosion through over cropping.