We see that the successive chambers of a spiral Nautilus or of a straigt Orthoceras, each whorl or part of whorl of a periwinkle or other gastropod, each new increment of the operculum of a gastropod, each additional increment of an elephant’s tusk, or each new chamber of a spiral foraminifer, has its leading characteristic at once described and its form so far explained by the simple statement that it constitutes a gnomon to the whole previously existing structure. And herein lies the explanation of that 'time-element' in the development of organic spirals of which we have spoken already; for it follows as a simple corollary to this theory of gnomons that we must never expect to find the logarithmic spiral manifested in a structure whose parts are simultaneously produced, as for instance in the margin of a leaf, or among the many curves that make the contour of a fish. But we must look for it wherever the organism retains, and still presents at a single view, the successive phases of preceding growth: the successive magnitudes attained, the successive outlines occupied, as growth pursued the even tenor of its way.
The spiral reveals itself as the dominant formal motive. Although the spiral as a form is known to have numerous symbolic and cosmic meanings, in the context of Robert Smithson's iconography we should rather search within the realm of crystallography. The artist had used the form before in a piece titled Gyrostasis. The term itself refers to a certain crystal extension known as screw dislocation, the mathematical ordering of spiraling hexagonals around a void. This means that there is no single vanishing point. As mentioned before, Smithson intended to show that the Renaissance perspective was not the only way to create a true representation of reality; and that it was only a mental construct, a conceptual framework based on the scientific laws of absolute space and time. Albert Einstein's discoveries in physics had long shown that time and space were relative. And by now, quantum physics had even proved that there was another, invisible reality behind the visible world, governed by different laws.
M.J.M. Bijvoet, Greening of Art, (chapter 5: Robert Smithson: Art as Entropic Phenomenon)