In proceeding to consider still farther the physiology of rocks, the author proposed in this communication to confine himself to the illustration of

1. The Columnar Structure.—After enumerating examples of this structure, as occurring in the neighbourhood of Edinburgh, in cannel coal, sandstone, clay, ironstone, clinkstone, claystone, greenstone, and basalt, he exhibited examples of similar appearances in oven soles and fragments of the walls of vitrified forts. The ordinary explanation of this structure as the result of cooling from a state of fusion he pointed out as unsatisfactory, even in the case of basaltic pillars, and inapplicable to similar appearances as occurring in sedimentary rocks.