Early twentieth-century weird tales reward ecocritical consideration of the ontological positions they take on the place of humans in a more-than-human world. This chapter examines Algernon Blackwood’s 1912 short story “Sand” as an eco-weird fiction. In this story, the Eastern Sahara in Egypt is endowed with its own vitality and agency, establishing the desert as an entity with which humans have an ecological relationship, as well as demanding recognition of its Ka, the ancient powers concealed behind the veil of the everyday. The desert’s distinct form of life is presented in terms of its geological age, climatic changeability, and the movement and elasticity of sand itself, and reaches a tipping point that threatens to overwhelm the human world when an occult ceremony attempts to channel it into the present. The protagonist’s encounters with sand stimulate an ontological reorientation based on knowing the desert as much through the spirit as the senses and the mind; the Weird, like twentieth-century “crisis disciplines”, draws on multiple forms of knowledge when addressing human-nature relationships. Ontological reorientation in Blackwood’s eco-weird leads to an understanding both of continuity and reciprocity between the human and the other-than-human, and of the potential impacts of human interference.