The Evidence for the Linear Order of the Genes.

leave only gas as interstitial material. This is, however, not the only possibility. It is not difficult to conceive of a distribution of forces in the heterogeneous surroundings of an igneous mass such that locally the liquid might be sucked out of a crystalline mesh, which would acquire a miarolitic texture, temporarily, at least. The consequences of this action would normally differ in no essential particular from those produced by simple squeezing out of the liquid. It is probable, however, that this sucking action could be operative at a very late stage of crystallization when squeezing out of liquid may be impossible or at least very unlikely. The kinds of liquid that form some of the alkaline rocks may perhaps be removed in this manner from quartz-mica rocks at a very late stage of their crystallization and possibly only such action can effect the separation of these liquids.' In certain regions of the earth's crust where tangential extension is the dominant expression of the forces acting (Atlantic structures) the development of alkaline rocks might be a prominent feature though the conditions requisite to their formation would undoubtedly occur locally elsewhere.