NECK, that part of the body which connects the head with the trunk (see ANATOMY : Superficial and Artistic). The word is transferred to many objects resembling this part of the body in shape or function ; it is thus applied to an isthmus, or to the nar rowest portion of a promontory, to the narrow part of a musical stringed instrument connecting the head and body, as in the violin, or to a narrow pass between mountains, which in the Dutch form nek, appears in place-names in South Africa. In architecture, the "neck" is that part of the capital just above the "astragal," and the term "necking" is applied to the annulet or round, or series of horizontal mouldings, which separates the capital of a column from the plain part or shaft. In Romanesque work this is some times corded.
In Geology, the term "neck" is given to the denuded stump of an extinct volcano. Beneath every volcano there are passages or conduits up which the volcanic materials were forced, and after the mass has been levelled by denudation there is always a more or less circular pipe which marks the site of the crater. This pipe, filled with ashes or lava, is the characteristic of a volcanic neck. Many instances are furnished by the geological history of the British Isles. In Derbyshire, Fife, the Lothians and the Glasgow district the remains of Carboniferous volcanoes occur in every state of preservation. Some have the conical hills of lavas and ashes well preserved (e.g., Largo Law in Fifeshire) ; others retain only a small part of the original volcanic pile (e.g., Arthur's Seat, Edinburgh; the Binn of Burntisland) and of the larger number nothing remains but the "neck" which shows where once the crater was situated.
In regions of former volcanic activity necks are the most per sistent of all volcanic structures, because the active volcanic mag ma is located deep within the earth's crust, and the pipe by which it rises to the surface is of great length and traverses a great thickness of strata. This extensive pipe was usually vertical, and nearly uniform in diameter for great depths; when exposed by de nudation, it has a circular ground plan, or if shown in vertical section (or elevation) in a cliff is a pillar-shaped mass crossing the bedding planes of the strata nearly at right angles. It ter minates upwards in the remains of the volcanic cone and com municates below with the reservoir from which the lavas were emitted, represented in most cases, where it has been exposed, by a large irregular mass (a batholith or boss) of coarsely crystalline igneous rock. The site of such a neck is generally indicated by a low conical hill consisting of volcanic rock, surrounded by sedi mentary or igneous strata of a different kind. The low cone is due to the greater hardness and strength of the volcanic materials and is not connected with the original shape of the volcano. Two
splendid sugar-loaf cones known as the Pitons of St. Lucia in the West Indies, rising from the sea with almost vertical sides to a height of nearly 3,000ft., are old volcanic necks. In Texas, New Mexico, Arizona, California and many of the western states of North America, geologists have observed conical volcanic hills having all the features which belong to necks.
Where the volcanic rocks are soft and easily disintegrated the position of a neck may be indicated by a cup-shaped hollow; this is the case with some of the diamond-bearing basic pipes of South Africa. Examples are the Kimberley diamond mines. The blue ground (or serpentine breccia) occupies great pipes or funnels, cir cular in outline with nearly vertical sides, extending downwards to unknown depths ; these are the necks of the old volcanoes.
The size of necks varies considerably; the smallest may be only 20 or 3oyd. in diameter, the largest are several miles. In this re spect they resemble active craters, but no necks have been met with on the earth's surface with dimensions approaching those of the so-called "craters" of the moon.
Occasionally a whole neck is composed of solid crystalline rock representing the last part of the magma which ascended from the underground focus and congealed within the crater. In Mont Pelee, for instance, the last stage of the eruptions of 1902 to 1905 was the protrusion of a great column of solidified lava which rose at one time to a height of goof t. above the lip of the crater, but has since crumbled down. The Castle Rock of Edinburgh is a neck occupied by a plug of crystalline basalt. Necks of this kind weather down very slowly and tend to form prominent hills.
After the eruptions terminate gases or hot solutions given out by deep-lying masses of molten rock may find a passage upward through the materials occupying the crater, greatly modifying their mineral nature and laying down fresh deposits. A good example of secondary deposits within a volcanic neck is provided by the Cripple Creek mining district of Colorado. The ore-bearing veins are connected with volcanic rocks and part of these occupy a vertical circular pipe which is a typical volcanic neck. A phono litic breccia, greatly altered, is the principal rock, and is cut by dikes of phonolite, dolerite, etc. The country rock is mostly gran ite and gneiss, and blocks of these are common in the breccia. A large volcano was built up in Tertiary times on the granite pla teau, and has since been almost entirely removed by denudation. The gold ores were carried upwards by currents of hot water de rived from the volcanic magma and were deposited along cracks and fissures in the materials which occupied the crater, and also in the surrounding rocks (see VOLCANO). ( J. S. F.)