No abstract

It has been suggested that a substantial amount of heat energy could be extracted from dry hot rocks near the earth's surface by circulating a fluid through large hydraulic fractures. However a theoretical analysis of propagation and closure of hydraulic fractures subject to realistic stress gradients indicates an upper limit for the size of a stable fracture. For example, if the vertical gradient of the least principal stress exceeds the unit weight of the fluid by ∼100 dynes/cm³ a stable vertical fracture in granite held open by fluid pressure may not be more than ∼2 × 104 cm high. This limit should be taken into account in the design of dry hot rock heat recovery systems.

No abstract

No abstract

An assemblage of Middle Cambrian Atlantic faunal province trilobites has been found in the rocks of the Carolina slate belt near Batesburg, South Carolina. Geologic and paleomagnetic data suggest that the Carolina slate belt and the adjacent Charlotte belt constitute an exotic terrane that was accreted to North America in early to middle Paleozoic time.