The Volcanic Rocks of Lower Silurian age in the Lake District are interesting in the highest degree on many accounts, and not least so on that of the extreme metamorphism which they have undergone, partly by the deep burial they suffered during the period between the close of the Lower Silurian and the Old Red, when they were once more largely uncovered, and partly by that neverceasing action of infiltration, decomposition, solution and replacement to which all rocks are subject during the course of geological time, but to which rocks of an originally volcanic origin seem specially subject.

If there is one feature in this metamorphism of the Cumberland rocks more prorainent than another, it is the large degree to which chlorite has been developed among them, and the universality of its occurrence.