Page:A Treatise on Geology, volume 2.djvu/110

 96 One of these cases has been amply treated by Macculloch, in his account of the Island of Skye; examples of it may also be seen in the Island of Arran. The reader will understand the circumstance alluded to by consulting fig. 81., where (d) represents a vertical mass of igneous rock (greenstone in Skye, pitchstone in Arran) filling & fissure in the stratified rocks, (s) and (b) an interposed bed of the same igneous rock forced in a liquid state between two strata originally contiguous.

The second case is exemplified in the basaltic formation of Antrim, where several successive layers of melted rock, the fruit of many successive volcanic eruptions, are heaped one upon another as they were originally poured out upon the chalky bed of the ancient sea.— Another example is furnished by the volcanic rock called "toadstone ," which in Derbyshire lies in one or more stratiformed masses between the beds of mountain limestone, as probably it was originally effused on the surface of the lower bed. The upper surface of the toadstone is said to be remarkably undulated. A third example is found in the region round Crossfell, where a basaltic formation, called the "whin sill," is widely spread in the midst of the limestones and sandstones, over some of which it appears to have poured as a submarine current of lava, while through and amongst others it was