The Earth's thin crust of organic matter and the still thinner crust of the spirit is the most concentrated, the most suggestive part of the cosmos. It in every way exceeds itself by pointing above its horizontal surface towards vertical transcendence. However, it can never leave itself behind and always carries itself with itself in every ascent. Poetry attends to the resultant human diagonal.
--from the preface to the first sequence, On the Diagonal: Metaphysical Landscapes