INTRUSIVE FEATURES Batholiths Large domeshaped reservoirs of Magma

INTRUSIVE FEATURES � Batholiths- Large dome-shaped reservoirs of Magma, located deep within the earth’s crust. � Laccoliths and Phacoliths- smaller reservoirs of magma � Sills- masses of magma injected or flowing horizontally to the bedding plane. � Dykes- sheet-like intrusions of magma lying across or diagonally at an angle to the bedding planes.

CHANGES TO INTRUSIVE VOLCANIC FEATURES OVER TIME � � Batholiths- if the overlying rocks are denudated, they form steep sided rounded hills or uplands on exposure on the earth’s surface e. g. Canadian Shield. Laccoliths- exposed through denudation of overlying rocks to form conical-shaped hills or mountains such as Henry Mountains in UTAH, USA.

� Sills- through denudation theey are exposed to form scarps and waterfalls. A tilted sill may form a waterfall or spring as it impedes the flow of ground water. Thy are common in Guyana in the Pakaraima Mts. and Mt. Roraima. Also found below Malali Falls on the left bank of the Demerara River.

Dykes- They are exposed by denudation, forming a ridge if it is more resistant than the surrounding rocks or a depression, if it is less resistant. Some dykes form springs and waterfalls.

Volcanic Plugs Acidic lava sometimes solidify in the vent of volcanoes. When the composite con becomes dormant erosion begins to destroy the cone. The cone is stripped away leaving a plug standing as a steep, semicircular pinnacle in the vent or pipe. e. g. Pitons in St. Lucia

The Pitons in St. Lucia