Helping San Diego, California and beyond since 1997.
Do you need
volunteer, community service, work, military or court hours?
|
|
Helping San Diego, California and beyond since 1997.
|
|
Click here and add this page to your favorites!
|
Encyclopedia Britannica - Main :: KRO-LAP |
|
|
LACCOLITE (Gr. XhKKOS, cistern, XLOos, stone) , !in geology, the name given by Grove K. Gilbert to intrusive masses of igneous rock possessing a cake-like form, which he first described from the Henry
great
Henry
diameter and range in thickness up to about 5000 ft. The cause of their peculiar shape appears to be the viscosity of the rock injected, which is usually of inter-mediate character and comparatively rich in alkalis, belonging to the trachytes and similar lithological types. These are much less fluid than the basalts, and the latter in consequence spread out much more readily along the bedding planes, forming thin flat-topped sills. At each side the laccolites thin out rapidly so that their upper surface slopes steeply to the margins. The strata above them which have been uplifted and bent are often cracked by extension, and as the igneous materials well into the fissures a large number of dikes is produced. At the base of the laccolite, on the other hand, the strata are flat and dikes are rare, though there may be a conduit up which the magma Las flowed into the laccolite. The rocks around are often much affected by contact alteration, and great
Gilbert obtained evidence that these laccolites were filled at depths of 7000 to Io,000 ft. and did not reach the surface, giving rise to volcanoes. From the effects on the drainage of the country it seemed probable that above the laccolites the strata swelled up in flattish eminences. Often they occur side by side in groups belonging to a single period, though all the members of each group are not strictly of the same age. One laccolite may be formed on the side of an earlier one, and compound laccolites also occur. When exposed by erosion they give rise to hills, and their appearance varies somewhat with the stage of development.In the western part of South America laccolites agreeing in all essential points with those described by Gilbert occur inconsiderable numbers and present some diversity of types. Occasionally they areasymmetrical, or have one steep or vertical side while the other is gently inclined. In other cases they split into a number of sheets spreading outwards through the rocks around. But the term laccolite has also been adopted by geologists in Britain and elsewhere to describe a variety of intrusive masses not strictly identical in character with those of the Henry Mountains. Some of these rest on a curved floor, like the gabbro masses of the Cuillin Hills in Skye; others are injected along a flattish plane of unconformability where one system of rocks rests on the upturned and eroded edges of an older series . An example of the latter class is furnished by the felsite mass of the Black Hill in the Pentlands, near Edinburgh, which has followed the line between the Silurian
The term laccolite has also been applied to many granite intrusions, such as those of Cornwall
wall
End of Article: LACCOLITE (Gr. XhKKOS, cistern, XLOos, stone) If you wish, you can link directly to this article.
<a href="http://jcsm.org/StudyCenter/Encyclopedia/KRO_LAP/LACCOLITE_Gr_XhKKOS_cistern_XL.html"> LACCOLITE (Gr. XhKKOS, cistern, XLOos, stone) </a> |
|
|
(Previous) LACCADIVE ISLANDS |
(Next) LACE (corresponding to Ital. merletto, trina; G... |
|
Sponsored Advertisements