gold and diamonds in unexhaustible plenty

?Other poets display cabinets of precious rarities, minutely finished, wrought into shape, and polished unto brightness. Shakespeare opens a mine which contains gold and diamonds in unexhaustible plenty, though clouded by incrustations, debased by impurities, and mingled with a mass of meaner minerals.?

?Samuel Johnson, from his Preface to Shakespeare. Samuel Johnson: Rasselas, Poems, and Selected Prose, edited by Bertrand H. Bronson, 1958.