On Fluorite and Other Minerals in Lower Permian Rocks of South Durham1

During the past two years several core-borings have been put down in South Durham in order to prove extensions of the Productive Coal Measures. In passing through the cover of Magnesian Limestone, here up to 300 feet thick, quite the most arresting feature was the presence of innumerable cavities of irregular distribution. These are especially characteristic of the Lower Limestones, and are of all sizes from tiny geodes almost completely infilled with calcite to gashes which cut deep into the heart of the 6 in. core. They are usually lined with calcite in a variety of forms; far more rarely there are other minerals among which fluorite and barytes seem to be the most abundant.