Complex sentence: In 1923 the petrologist Herbert Henry Thomas identified that bluestone from the hills corresponded to that used to build the inner circle of Stonehenge, and more recent geologists have identified Carn Menyn, sometimes called Carn Meini, as one of the bluestone sources.
Split into simpler sentences: In 1923 the petrologist Herbert Henry Thomas identified that bluestone from the hills corresponded to that used to build the inner circle of Stonehenge, Thomas, H.H.1923. Antiquaries Journal 3,239-260 and more recent geologists have identified Carn Menyn, sometimes called Carn Meini, as one of the bluestone sources.