exhaustlessly

We stopped at Virginia for three days, -- saw the California of '49 reënacted in a feverish, gambling, mining town, -- descended to the bottom of the exhaustlessly rich "Ophir" shaft, -- came up again, and resumed our way across the Sierra.

The Atlantic Monthly, Volume 13, No. 78, April, 1864 Various

Acadians, and the prudent Scot found himself the richer by twenty acres of exhaustlessly fertile meadow, worth a hundred dollars an acre any day.

Earth's Enigmas A Volume of Stories Charles George Douglas Roberts 1901

At the falls of the Roanoke, of the Tar river, on the rapid declivities of Haw and Deep rivers, on never-failing streams in Cumberland and Richmond counties, on the enormous forces of the two Catawbas, and perhaps elsewhere, a second thought would never be given to the application of any other power than that so exhaustlessly provided by nature and so easily and economically controlled.

North Carolina and its Resources. North Carolina. Board of Agriculture. 1896

The forest, the deep, vast forest of oak and ash and gum and ghostly sycamore; the forest, tangled with a thousand binding vines and briers, wattled and laced with rank blue cane -- sure proof of a soil exhaustlessly rich -- this ancient forest still stood, mysterious and forbidding, all about the edges of the great plantation.

The Law of the Land Emerson Hough 1890

Dorcas she is exhaustlessly competent, but I like my share of it and of course Dorcas likes hers, for Dorcas "raised" George, and

A Horse's Tale Mark Twain 1872