Elizabeth Cary Agassiz, Louis Agassiz: his life and correspondence, third edition

[758] tracts of the valley to the north of it free of ice, so that large glacial lakes could be formed, and seem, indeed, always to have existed along the retreating edge of the great southern glacier. The natural consequence is that there are everywhere stratified terraces without border barriers (since these were formed only by the ice that has vanished), resting at successively higher or lower levels, as you move north or south, upon unstratified drift of older date; the northernmost of these terraces being the oldest, while those further south belong to later steps in the waning of the ice-fields. From these data I infer that my suggestion concerning the trend of the strike upon the polished and glaciated surface of the vicinity of Talcahuana, alluded to in the postscript of my last letter, is probably correct. . . .