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Most rock samples brought back to Tucson from, say, the Colorado Plateau, can be ignored: diminutive, drab, obscure …inadequate in capacity to reflect the grandeur and three-dimensionality of in situ towering cliff exposures supported by Tapeats, Redwall, Supai, Coconino, Kaibab, Kayenta, Navajo, Wahweap, or Claron. However, the slabs in front of the Helen S. Schaefer Building have a mass, length, and utility that can’t be dismissed. These oversized parallelepipeds were quarried, transported, and placed without compromise, without cracking, without breaking, without scuffing. They were treated well. Someone went to the necessary trouble and expense, for as outside art these slabs align the mind for inside discovery.
We are struck by the structure, geometry, symmetry, and spacing of these lines of expression. They point us in the right direction. They support us as we climb aboard. Perhaps with a book in hand we sit on an ancient shoreline reflecting interference ripple marks, geometric expressions of which are more complex than normal because they were fashioned by competing agents, both wind and water, operating along different directions. Thus these ripple markings are not “textbook” linear, not even systematically curvilinear, but rather splotchy. Also on the bedding there are black dendrites, patterns caused by the chemical imprint of groundwater coming to rest after having moved through the permeable sandstone and leaving these black fern-like textures, the preferred precipitation texture of manganese dioxide.
Most delightful to me are the flanks and ends of the bench slabs, which are natural fracture surfaces, or natural joint surfaces, whose orientations (if seen in place, in situ, in bedrock) would give orientational insight regarding regional tectonic tensile-stress directions that once operated. There is an ornamentation on these surfaces, both hackles and ribs, that reflects the directions in which the fractures propagated—at half the speed of sound—when the rock was deeply buried.
It is special to have such long, joint-bounded blocks. The spacings of the joints are reflected in the widths of the benches and the lengths of the slabs, and these spacings disclose something about the elastic mechanical properties of the sandstone in responding to fracturing and in releasing strain energy. Sighting along them I find appealing the curviplanar nature of the joint flanks of the blocks. The subtle smooth changes in orientations are reflecting subtle smooth changes within the stress field in which the fractures propagated. The subtle curving softens the slabs, imparts grace, relieves the stiffness.
All in all, we see in the blocks the complexity and elegance we see in all natural systems, in this case emerging as a composite, first from the creation of textures in vulnerable materials by the force of flowing wind and water when the sand was still sand, and then to the releasing of pent-up strain energy (some call it stress) in strong materials after the sand became sandstone and the sandstone was forced to undergo ever-so-slight changes in length.
We ourselves know something about the combinations of vulnerability and strength, and of flow and fracture, in our own lives, in our own families, in our own societies, in our own histories. We are aware that both flow and fracture—in response to competing forces that mold and shape and split—always leave marks, some of which are visible, some of which are hidden internally. Elasticity and brittle “failure” (a geologist’s word for permanent, non-recoverable distortion) are, to be sure, common themes of narrative and poetry, and yet these shape-changing agents need not be viewed as destructive or limiting, but in concert with growth and life experience can serve to shape and adapt us for the singular constant in life: change, and nonlinear change at that. After all, these slabs never imagined that they would one day be here, but we are delighted they arrived here in the 270,000,000th year of their existence. They found a good home at the Poetry Center. Change was for the better.
by George Davis, Regents Professor, Department of Geosciences
These sandstones are named the Diamond Benches in recognition of a gift from the Diamond Foundation. A sandstone bench inside the Mary Dearing Lewis Garden is named in memory of John A. Hudak, Jr.