The interesting note by Mr. Strahan in the Geol. Mag. for September, 1887, on explosive slickensides, reminded me of some similar phenomena which were not of unfrequent occurrence near Dent Head and Ribble Head in Yorkshire.

In the limestone quarry from which the black marble of Dent is procured the workmen found that, when they were quarrying the lower beds and struck the rock with a pick or bar, fragments flew up into the air with greater force than, could be due to their blow and in an unexpected direction.