In 1973 Robert Smithson made a series of works he titled Slate Grinds. Each comprises a section of slate on which he incised a partial circle. These late works by Smithson encompass a number of his central interests: materiality, deep time, aerial views, a critique of extractive industries, and geological history. Through the Slate Grinds Smithson forges a direct connection with geologic time, mark-making through the geologic process of erosion. In a 1972 interview with Gianni Pettena, Smithson said, “As an artist it is sort of interesting to take on the persona of a geologic agent where man actually becomes part of that process rather than overcoming it.”

The Slate Grinds speak to Smithson’s parallel sculptural and drawing concerns. They are displayed on the floor as sculptures to be looked at from above, and have a clear line of drawing on their surfaces. He chose the material carefully for its geological history and for its use in construction. Slate is a metamorphic rock formed through volcanic activity upon sediments deposited around 550 million years ago, and it is extracted from the land in both quarries and open mines. Once unearthed it can be easily split and its durable nature has led to it being a key component in building construction.

From 1968 Smithson explicitly worked with materials that can be connected to the formation of our planet that are used for human advantage, and he used slate several times. In 1969 he developed an idea for an island made of slate and in 1972 an idea for an unrealized sculpture made of four slate circles, measuring eighty feet wide. In 1968 he created one of his earliest Nonsite sculptures from the material—Nonsite (Slate from Bangor, Pa.). 

Smithson’s Slate Grind #4 is in the collection of the Whitney Museum of American Art, New York. Holt/Smithson Foundation holds numbers 3, 5, 6, and 7 in its collection.