Speleothems, from the Greek words for cave and deposit, include the familiar descending stalactites, upward-growing stalagmites and more continuous sheets called flowstones.  They grow slowly, at rates of between 1 mm a year to 0.001 mm a year.   This growth can persist for many thousands of years before being interrupted.  As with trees, speleothems commonly display annual layers which may be visible when a sample is polished, or recognised through chemical analyses.  Ideally, a sample will accumulate regular, parallel layers,  allowing the investigator to study its growth through time, and see changes in environmental conditions. These speleothems grow in caves within limestone rock.  Typically the...