|
NECK (O. Eng. hnecca; the word appears in many Teutonic See also: part of the See also: body which connects the See also: head with the trunk (see ANATOMY: Superficial and See also: Artistic)
.
The word is transferred to many See also: objects resembling this part of the body in shape or See also: function; it is thus applied to an See also: isthmus, or to the narrowest portion of a promontory, to the narrow part of a musical stringed instrument connecting the head and body, as in the See also: violin, or to a narrow pass between mountains, which in the Dutch See also: form nek, appears in place-names in See also: South See also: Africa
.
In architecture, the " neck " is that part of the capital just above the " astragal," and the See also: term " necking " is applied to the annulet or round, or series of See also: horizontal See also: mouldings, which separates the capital of a See also: column from the plain part or a See also: shaft
.
In Romanesque See also: work this is sometimes corded
.
In Geology, the term " neck " is given to the denuded stump of an See also: extinct See also: volcano
.
Beneath every volcano there are passages of 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 See also: pipe which marks the site of the See also: crater
.
This pipe, which is filled with consolidated ashes or with crystalline See also: lava, is the characteristic of a volcanic neck
.
Active volcanoes often stand on the See also: sea-bottom and when the eruption comes to an end the volcano is slowly buried under layers of sediment
.
In tropical seas the See also: coral animals cover over the submarine volcanoes which rise nearly to the See also: surface and form See also: great reefs of See also: limestone around them
.
Should See also: elevation take place after long ages the removal of the overlying strata will bring the volcanic mass to See also: light, and in the normal course of things this will suffer denudation exactly like a See also: recent volcano
.
Many instances of this are furnished by the See also: geological See also: history of the See also: British Isles
.
In Carboniferous times, for example, before the See also: Coal-See also: measures were deposited, a shallow sea occupied the See also: southern part of Scotland and the See also: north of See also: England
.
Volcanic activity broke out on the sea-bottom, and many volcanic cones, both small and large, were produced . These have long since been uplifted and the superjacent strata denuded away over a large part of theSee also: area which they occupied
.
In See also: Derbyshire, Fife, the Lothians and the See also: Glasgow See also: district the remains of Carboniferous volcanoes occur in every See also: state of preservation
.
Some have the conical hills of lavas and ashes well preserved (e.g
.
Largo See also: Law in Fifeshire) ; others retain only a small part of the See also: original volcanic See also: pile (e.g
.
Arthur's Seat, See also: Edinburgh; the Binn of See also: 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 persisterlt of all volcanic structures, because the active volcanic magma Is located deep within the See also: earth's crust, and the pipe by which it rigs to the surface is of great length and traverses a great thickness of
strata
.
Many volcanic necks stand on lines of fault
.
In other cases have fallen down from strata once occupying part of the walls of the crater but now removed by denudation
.
The lava which rises and flows out from the crater leaves its trace also in the necks
.
Sometimes it forms thin beds or flows alternating with the tuffs and having the same See also: basin-shaped dip
.
More commonly it appears as the material filling fissures and pipes, traversing the ashes irregularly or rising as a central plug in the interior of the neck, and sending out branching See also: veins
.
Occasionally a whole neck is composed of solid crystalline See also: 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 See also: rose at one See also: time to a height of 900 ft. above the lip of the crater, but has since crumbled down
.
The See also: Castle Pock of Edinburgh is a neck occupied by a plug of crystalline See also: 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 See also: mineral nature and laying down fresh deposits
.
A See also: good example of secondary deposits within a volcanic neck is provided by the Cripple Creek See also: mining district of See also: 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 phonolitic See also: breccia, greatly altered, is the See also: principal rock, and is cut by dikes of phonolite, dolerite, &c
.
The country rock is mostly granite and See also: gneiss, and blocks of these are See also: common in the breccia
.
A large volcano was built up in See also: Tertiary times on the granite See also: plateau, and has since been almost entirely removed by denudation
.
The gold ores were carried upwards by currents of hot See also: water derived 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 . |
|
|
[back] NECHBET (Nekhbi, Nekhebi) |
[next] ALEXANDER NECKAM (1157-1217) |
There are no comments yet for this article.
Do not copy, download, transfer, or otherwise replicate the site content in whole or in part.
Links to articles and home page are encouraged.