the granitic bosses as parts of the mechanism of Palæozoic volcanoes. It will also be shown that among the intrusive rocks of the Tertiary volcanic series of Britain there occur bosses of truly granophyric and granitic material. Hence, though mainly what is called a "plutonic" rock, granite has made its appearance among the subterranean protrusions of volcanoes. [Footnote 35: M. Michel Lévy, _Bull. Carte Géol. France_, No. 35, tome v. (1893), p. 32. The view stated in the text is also that adopted by Prof. Brögger with reference to the granite of the Christiania district. "Die Eruptivgesteine des Kristianiagebietes."] It is no doubt true that many intrusive masses, which must be included under the general name of bosses, have probably had no connection whatever with volcanic action properly so called. They are plutonic injections, that is, portions of the subterranean magma which have been intruded into the terrestrial crust during its periods of disturbance, and have not been accompanied with any superficial discharges, which are essential in truly volcanic energy. It has been proposed to draw a distinction between such deep-seated intrusions and those which represent volcanic funnels.[36] If this were always practicable it would certainly be desirable. But the distinction is not one that can in every case be satisfactorily drawn. Even in regard to granitic bosses, which may generally be assumed to be plutonic in origin, the British examples just referred to have in all likelihood been connected with undoubted volcanic outbursts. Without, therefore, attempting here to separate the obviously volcanic necks of eruptive material from the probably plutonic bosses, I propose to describe briefly the general characters of bosses considered as a group of intrusive rocks, together with the phenomena which accompany them, and the conditions under which they may have been injected. [Footnote 36: M. Michel Lévy, _Bull. Carte Géol. France_, No. 35, tome v. (1893).] Bosses, whether of plutonic or volcanic origin, are frequently not merely single masses of eruptive rock, but are accompanied with a system of dykes and veins, some of which can be traced directly into the parent-mass, while others traverse it as well as the surrounding rocks. Hence the history of a boss may be considerably more complex than the external form of the mass might suggest. The petrographical characters of bosses link them with the other underground injections of igneous material, more especially with sills and laccolites. Indeed, on mere lithological grounds no satisfactory line could be drawn between these various forms of intrusive rocks. The larger the mass the more coarsely crystalline it may be expected to be. But the whole range of structure, texture and composition, from those of the narrowest vein to those of the widest boss, constitutes one connected series of gradations.