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Published online by Cambridge University Press: 15 September 2014
It is commonly believed by geologists, as well as by coal miners, that the inner faces of the rocks which enclose intrusive masses were at one time in contact, and that each of these surfaces is the counterpart in form to the other, from which it has been severed by the forces to which the injection of the intrusive mass was due. In the case of a sill, for example, this belief implies that the rock floor below the sill and the roof above it were in unbroken contact at some time before the sill was intruded, and that the floor and the roof have been forced apart to a distance equal to the thickness of the intrusive mass.
note * page 199 The questions raised are of a petrographical as distinguished from lithological character.
note * page 203 Why should these be called Xenoliths
note * page 220 See a paper by the present author, “On a Granite Junction in the Isle of Mull,” Geol. Mag., dec. iii., vol. ix. pp. 447–451 (1893).Google Scholar